Start with small steps, doing simple small things that you enjoy doing for yourself. Join a group of like-minded individuals with similar interests. Remind yourself that you have every right to make your needs a priority.

I hate Nike but, Just do it.
Whatever ever it is,
if you think you might like something,
Just do it,
take the step, swallow down any fear and insecurity.
There is no difference between someone who is brave and someone who acts brave.

Hopefully you're already out of the codependent situation, so that's 90% of the battle.

You can find support by googling and joining various local community groups that do what you already enjoy doing..hiking, kayaking, bird watching, biking, book clubs, etc.

Or volunteer to clean up a park, repair a national forest trail, serve meals in a soup kitchen, etc.

Hopefully, you're employed so you aren't financially dependent on your ex.