I guess they can if they embrace and are then run over by a steamroller so they are squished into one
It's never once worked out for me. I'm always the one that they love having as a best mate, but never want to take things further with. I've developed crushes on friends and brought up the subject of taking it to the next level on a number of occasions. Every single time, it was rejected.
So while I'm sure it can work for some people, I don't believe it's a universal possibility.
I have crush on my friend and she said she only see me as a friend but I'm still believing that we will end up together.
Should friends become lovers should be the question. you lose 2 things when it ends instead of one.
Perhaps friends are married or keep secret their intimacy with others. ....if not lovers elsewhere why didn't "friends" start out as lovers anyway ? Sure friends can be lovers. ...you both need to be age 18+