Wow, short questions long answers.
Here are a few things that are part of my moral code:

1.. Whatever you want to do is fine. It's not my place to judge you, nor yours to judge me.

2.. Myself, personally, I will not agree to be monogamous. If you need that, look elsewhere.

3.. The agreements I do make, I will keep.

4.. Everything is negotiable. Let's talk! What works for you? What works for me? What can we find that works for both of us?

So when we got married, in the Jewish not the Christian ceremony, by mutual agreement we left out some of the usual wordings about fidelity. Yes we both agreed to be true to each other. Not quite the same as "cleave only unto".

Ya don't miss a slice off a cut loaf!

I agree with the others here that you cut a deal with your spouse that you would not cheat. End of discussion.

And it always irks me when I hear someone say “All men cheat”. I have been married 27 years and had opportunities to be unfaithful (used to travel quite a bit conducting business with women). Was propositioned a few times, but I never came close. Not bragging in the least. Just making the point that men do exist who do not cheat.

It came from rights of inheritance and property initially, and it depends on what you agree to first. Also comes from possibility of disease , I don't want a companion I can't trust if your foundation is based on lies

My "moral feelings" in any relationship would have to be along the lines of what I thought each of us as a couple would want. Morality is not a dictated situation from a set source of info. Morality is different in certain parts of the world so it is a construct of society and not some imaginary god.

I prefer to concentrate on one person and have the same attention when it comes to sexual relationships.
I cheated on someone once, as a teen, and it felt awful, it’s not something I’d want to do again.
I also try to have a break between relationships to reconnect with myself and let the memories of things going sour/ romanticising that maybe we could have worked it out dissipate.
In the only poly relationships I’ve ever known about there’s always someone who feels they would rather be in a mono one. But some people are better at ignoring what their partner truly wants than others, relationships involve compromise. No one is perfect.

I think it is whatever the two of you agree to do. And things change over time, so that agreement has to be updated occasionally.

I don't think about "morals" at all. I just follow the golden rule, period.

I am up for anything consensual, and not for anything that hurts woman or she says no to.

I don’t consider this a moral issue

Let's be honest here, the reason marriage exists as a tradition is for the purpose of child rearing. Humans are a semi monogamous species, meaning we have members who are both monogamous and non monogamous, one of a few species that do this. When we were nomadic hunter gatherer tribes, this wasn't a big deal because the tribe was in charge of raising the young. After we formed societies and the concept of heritage came into existence, monogamy became important because you wouldn't want to give all your wealth after you died to someone who wasn't your offspring.

Raising a child is still expensive, and the desire to proliferate your own genetic information is deeply ingrained in our biology. Having your significant other violate a marriage can be deeply offensive because it effectively denies the other person the right to procreate, even if this only emerges in an unconscious way. Infidelity can destroy relationships which means that the two in the relationship have effectively wasted their time, that is inherently offensive, but not necessarily immoral.

Right now, my working definition of morality is informed consent. If all parties involved know what is going on and agree, the action is moral, so if a couple wants a polyamorous relationship, it's perfectly acceptable.

It's a personal choice and standard that you hold yourself to for the benefit of your own self assurance, and maintaining a strong and successful bond with your partner, I just posted a debate topic about polyamory and how I feel about and am waiting to see the defense. But as I feel about it in this moment some people who choose a non committal lifestyle will never feel the intensity of emotion of someone who has had their sights and feelings honed by a life of both discipline and rejection at times, those who flagellate and shack up with whoever pleases them at a given moment will never feel what I feel or connect as strongly as someone with focus and intention to their relationship decisions. That's my take, but I'm also willing to hear the point of a skeezer as well in an effort to understand the hedonistic viewpoint.

I've read through the comments and responses, and here are my thoughts. I'll try to cover what you seem to be driving at generally, while expressing my own personal views:

• I'm uninterested in marriage, and sexual infidelity isn't exclusive to marriage, so I'm going to ignore that part of the question.
• Sex isn't very important to me. While I enjoy aspects of sex, and I'm eager to please my partner, it's not something I really need the way most people seem to.
• I don't consider sex itself to be necessarily more intimate than other shared activities.
• My feelings about sex, though, aren't the only ones to consider. I have a partner and her feelings are important. It doesn't matter where those feelings come from — religion or advertising or legality or whatever — all that matters is that I know how she feels and I've accepted those feelings as valid by entering into a romantic relationship with her.
• Despite my own adherence to sexual fidelity, I acknowledge that I don't own my partner and that she alone controls her body and behavior. I accept that she has the right to make her own decisions, though if she has sex with someone else — knowing how she feels about it — we may need to have a discussion about what it means for our relationship and our future.
• What people in any relationship decide is up to them, as long as they're mutually agreeable to whatever terms are set forth. This is the crux of self-determination.
• My values in this are commitment, trust, and self-determination. I don't want to hurt my partner, so I won't do anything to betray her trust. And I know she doesn't want to hurt me, so if she had sex with someone else I'd know something else was going on and I'd want to explore that with her.
• Notice that my values here have nothing directly to do with sex. This isn't about sexual morality for me. And I think for many people sex is just the vehicle for deeper aspects of the relationship, but they become entwined and aren't easily distinguished.
• Nobody has explicitly told me what to think regarding my values. I contemplate ethics a lot and consider what sort of person I want to be and what behavior is consistent with my values. That's not to say I'm perfect and always live up to my convictions, but it's the standard I set for myself and strive to attain.
• If you still want to know why trust and commitment are important to me in the context of a relationship, or why I think self-determination is so vital in life, I really can't help you — that's just too big an undertaking. I'd simply recommend reading some philosophy on ethical schools of thought, with a bit of focus on stoicism (where I feel I mostly fit), and suggest also looking into some psychology and anthropology regarding interpersonal relationships, to just understand how society has developed and what behavior is conducive to a healthy relationship and what behavior is detrimental to a relationship (romantic or otherwise).

So are you referring to moral/ethical codes or just sex?

My morality on it is the effect it has on the children. Who comes first?

Do or cause no harm and you should be good to go.

Married twice. Both times by justice of the piece (court). No church involved.