Should I see him or not?? 😔

I have an old friend coming to town to surprise his mom for Mother's Day and he wants to meet up and see each other. He said he'd understand if I didn't want to, but I also feel like I should...in respect of our past ties.

In high school we were kind of FWB for a few months, lightly stayed in touch over the years and I've hooked up with him twice in the recent years. Once while out in California for a friend's wedding and once over the Christmas in 2016. The January after that Christmas, I found out I was pregnant with his baby. We were nothing like a couple and I was nowhere near even being able to support myself, let alone a child. He supported me wholeheartedly throughout my decision to have an abortion, helped me pay for it, and was there for me every step of the way. This baby is what I mean by "our past ties". The few weeks before my abortion, I was secretly happy to carry a little part of us. I knew I couldn't get attached to it but it's something that'll always tie me to him. We have completely mutual respect for each other and he'll always have a special place in my heart and life.

My ex and I are in a weird place. Broke up months ago but still act like we're together. So, unofficially he's my boyfriend I guess.

The other guy messaged me earlier today to tell me he was coming to town soon and if we could meet up. I don't know how to bring this up with my guy. I wouldn't want to keep it from him if I did see him because I find that disrespectful. But I do feel like a part of me needs to see him (baby daddy), because the last time I saw him, he left me with something that will always be a huge part of my life. And it was an important thing to him too. He'd never gotten anyone pregnant before, and he still checks up on me from time to time to see how I'm doing because he knows it was really hard on me.

Anyway, should I not even give him coming to town a second though? Or is it understandable that I want to see him after everything that's happened? And how do I bring it up with my boyfriend/ex?