
Let me get a crack at it with my personal analysis:
If this latest arc showed me anything, it’s that it is very likely that for as many times as TJ manipulated the situations to keep Ian at his side, Ian continuously played the role of the only person TJ could rely on. Ian has a vague sense of satisfaction/he’s almost smug at the thought that TJ actually NEEDS him (chapter 15 for reference). It’s because of this same idea that TJ can’t just let him go. He believes it so deeply that he probably thinks he wouldn’t be able to make it without Ian at his side. Because Ian also believes this and worries about him, he didn’t listen to TJ telling him to stay away from the funeral.
This must have occurred more than once over the course of their relationship. They’ve spent so much time relying on each other as friends, family and lovers that they’ve developed a codependency that led Ian not to think of the possibility that TJ loved him too much to put him in danger. So while Ian did try to leave a few times, think about it this way: if TJ wasn't part of the gang, Ian wouldn't be so plagued with this desire to stay away for long periods of times. But the whole thing is so deeply entangled together that it's become difficult for him to even realize that he's in love with TJ.
Regardless of what led Ian to want to leave, here’s a formula for you:
The way TJ was able to walk away from Ian to keep him safe = the way Ian is ready to stay by TJ to make sure he's safe.

Yeah, they also suck at communicating with each other in a healthy way. I think TJ walking away was a good thing because it means he knows on some level that he can take care of things without Ian constantly being in his back.
About the funeral stuff: going to the funeral is basically like walking into a den of gangsters. Ian walked away from that gangster life, but with the death of Jason, the situation is dangerous because anyone with a high enough level within their whole criminal syndicate is basically a threat. That means TJ who is high enough in ranks is in constant danger (hence the car accident) and having Ian there would put him in danger as well. That’s why TJ asked him to stay away, but Ian didn’t listen. So everyone who knew Ian back when he was active as a gangster, could just rope him back into dangerous situations. Case and point: it looks like they might use Ian to draw TJ back out in the open.
3rd time reading this story and I still don’t get what Ian is for Tj and what Tj is for Ian. Do they see each other the same ? What is Ian so afraid of that keeps him looking for Tj ? I thought Ian wanted to get away from Tj but Tj kept preventing him from doing so ? I must be reading with my ass bc ain’t no way I have this many questions unanswered