Sometimes my (23f) friend (30m) acts selfish and i don’t know how to think about it?

I have a friend (since a few months) and we’re both diagnosed with adhd. I also have cptsd from childhood and suspect mild autism, so very inexperienced with relationships in general. Looking for advice, sorry this is a bit long, i try to keep it short.

This friend has a long-term girlfriend (i know her), but when we go out together hes always seeking out and talking to the girls. But he does not want to talk with her about an open relationship like i suggested. One time he went from a gathering to the home of one (she invited him), though he says nothing happened. Another time he got very focused on a girl, we later went to the bar and he wanted to take her to a club. But there was another dude and he asked me to distract him and then go with them. I was already down + tired, because i didn’t connect with anyone like always, but agreed first. But his restless behavior got me and when we got out i just left them and went back in. I felt really used, left out and reminded of my loneliness, i went home crying. The next day we talked, he didn’t apologize but gave me (forced) advice about not assuming that the world is bad (which is what I feel strongly in situations like that, and i admittedly did get worked up over the course of the conversation), and also said that he doesn’t respect triggers/trauma. I just felt disrespected again.

Recently i made a joke in front of a girl where i mentioned his gf (she even had left just earlier). He denied having one? Then later with another person i made another joke about him denying it. He texted me at 3am saying that was really shitty of me, it embarrassed him in front of the 2nd person who’s important to his business, that i have to apologize (i did because i didn’t want a fight..), that it was his business to tell about his gf and i have to respect that. Accusing me why i did it (it was really just a joke). This gave me a really bad feeling. Ive decided to distance myself a bit.

But he’s given me advice about some things too. It’s also hard for me to make friends and find people that vibe like me. I don’t think he’s a bad person (he is nice too), but i don’t know how to think about his shitty behavior both in regards to his gf and me. I agree his relationships are not my business, i don’t even know how ok he acts wrt them, but i find it really inconsiderate to his gf. I also don’t want to be blamed over his behavior. I know he’s impulsive and looking for stimulation. But i really don’t know how to integrate behavior like that into my view of him and people. How okay is it and what are ways for me to think about it? Thanks for reading.

TL;Dr: i am very inexperienced with relationships and don’t know how to think about inconsiderate behavior by a coupled friend who uses me to get with girls