Update for those who remember

I made a post about crushing on my ex boyfriend's best friend. Mind you my ex and I ended things about 4 1/2 years ago. Lasted 3 years, very bad relationship, veryyy abusive and toxic and just overall a bad situation. Recently I've been talking to this guy who happens to be his best friend and we're reallyyyy into each other. Same sense of humor, we enjoy a lot of the same things, the only thing is that he's hesitant to pursue anything because he thinks it'll make him feel weird. We made plans to hang out yesterday but he backed out the last second because like I said, he doesn't wanna make it weird between him and his friend (my ex). Also kinda feels like when he talks to me he forgets I'm his friend's ex girlfriend until he REALLY starts thinking about it you know what I mean? As far as I know my ex doesn't give two shits about me. He doesn't cross my mind at all anymore and I'm sure he feels the same about me. But I get it, it is a weird situation. I just wish he would say fuck it and pursue this thing we have going on because I really do think it could be something really really awesome, and I feel like he knows that too. He's just not sure how my ex would feel about it. I don't wanna push anything and make him feel pressured but I also don't wanna let it go. He's been considering trying to hang out with me and I'm hoping he realizes it wouldn't be as big of a deal as he thinks it is? I feel totally helpless But I don't know how to pursue things with him without crossing any boundaries you know? Any advice?? ☹️