Should I leave?

First off, thank you guys so much for your response. I really do appreciate it.

Him and his ex have been separated for about 5 years now. He told me the reason he’s not divorced is because he doesn’t have the money for it. I asked him why he never told me and he said he didn’t want me to think less of him. I am the easiest person to talk to and I never judge, which he knows.

They do have a son together and coparent well. The baby his ex is pregnant with is not his. It’s her boyfriend’s.

I’ve been with my boyfriend for 3 years-living together for 2.5 years- and he just told me the reason he hasn’t proposed to me is because he’s still married and it’s also the reason he’s hesitant about having a baby. I’ve been wanting a baby for a year now and he never told me anything. He told me this tonight and I’m still trying to process everything. I don’t know how to feel and I’m thinking about leaving.

Side note: His ex is in a relationship and is currently pregnant. I added that just in case you guys think it’s a cheating thing.