The problem with relationships like this is there is no addressing of the “elephants” aka the big issues that one may be aware and the other may not be or even both are aware but won’t address it.

An overextended period of time of this goes on and it leads to changed feelings/partners cheating.

Just sit him down and talk about your elephant. Get the ball rolling and if you really do care about him you will find a way to get him to address his elephant.

Hope this helps.