So, I’m going to play devil’s advocate here for a moment.
I was in a toxic, crazy relationship for 7-8 years. We were together, apart, if I dated someone else he needed me back. I was crazy about him and couldn’t imagine a life without him. It was insane and wonderful and awful. I finally gave it all up when I met Husband. I knew that I had to commit to him if I was going to date him at all b/c we had mutual friends – I couldn’t take the relationship lightly if it started.
Ex dude was dating someone behind my back at that point (well – at that point I knew about her, we weren’t speaking, I hated him, etc). I started dating husband.
Ex dude and I are now friendly. There was a lot of hurt and anger that we both felt and we needed time to resolve it, accept it, and move on. I accepted that he wasn’t the one for me and moved on. He accepted that I may have been the one and he ruined it and accepted that and moved on. We both care about the other and speak on occasion via text/Facebook. He wished me the best on my wedding day. I will always care for him and wish the best for him.
I will admit I miss being close friends with him. We had our “things” no one else ever got. No one else would want to kill some vodka and play Mario Party all night with me! But he was not the one for me.
My husband was at first very put off by our friendship (as we became friends again while dating Husband). But I was always very open about it, I didn’t hide anything, if I happened to run into Ex when visiting friends (we no longer live in the same town) I would tell him, etc. Now he accepts it. It isn’t his favorite, he doesn’t love it, but he understands it.
So I think it’s a matter of really assessing your relationship and trust. When he says “why” do you believe him? Do his actions line up with his words? HAs he cheated in the past? Do you think he would, with her? Or do you just think it is weird he would talk to an ex at all? You know him better than us, some of your answers sound like he is very defensive and not acknowledging your feelings as valid (they are valid!). If anyone you are in any type of relationship says your feelings aren’t valid (whether overreactive or not) I think it’s a red flag. Feelings are feelings – you can’t control them. They may be crazy or unfounded or whatever, but they are 99% of the time valid and mean something.
Is it possible for him to be innocently reaching out to her? Yes. Does it seem innocent in this situation? Hard to say from the Internet. Best of luck to you!