When a guy clearly doesn’t Love his girlfriend but won’t end things?

I know this sounds bad

This guy friend of mine and I have began getting closer. He has a girlfriend who he’s been in a relationship with for like 3 years.. I too was in a relationship for over a year which just recently ended.

While we were stricktly friends (as both of us were in our own relationships), he often expressed disinterest and a lack of enthusiasm about his girlfriend. Particularly to me, he would talk about how his girlfriend is alright looking, how he SOMETIMES loves her, how she’s annoying, how he does not truly want her.

I made nothing of it, as he was just my friend and I clearly wasn’t interested in him romantically

Ever since my relationship ended, which was about a month ago, him and I have gotten “closer” in a sense where we message almost every day and talk often.. he’s been “flirty” and has been acting like a guy who has a crush on a girl

And now that he knows I’m single, he’s been bringing up the not wanting to be with his girlfriend thing up more often... and has been messaging me more often

BUT clearly he’s still in a relationship and she’s his girlfriend (like once a week,,, if I may add)

So what does this sound like and what do I do in my situation if I actually like him more than a friend and would be interested if he was single.