If you are happy 90% of the time, then you just need to find a way to handle the other 10% of the time (his argumentative tendencies). You may/may not want to break with him further down the line, but until that time comes, you just need to find a way not to get drawn into his baiting for an argument.
I am one of those responsible types who can easily get drawn into the fixer/mothering role. Knowing what I now know, I would never do that again. The time, energy, money and opportunities I've wasted making other people's dreams come true! People who didn't really care about me when the chips were down. I am not referring to reasonable support of a partner who needs help, of course. Now I am burned out. Don't let this happen to you.
If you recognise any of yourself in my description of myself, you will find it very difficult to keep things casual and detached whilst still seeing this man. It can be done though. In fact, it may be a good learning experience for you in how to do this. It sounds like you have plenty to cope with already, so you don't have time to get drawn into these discussions with your BF. Your time and energy is precious.
I'd think of some deflection phrases to use in rotation every time you see this behaviour starting up. Just cite tiredness/preoccupation with other issues as to why you cannot indulge him at the time. Eventually, hopefully, he will learn that he can flex his debating muscles elsewhere, leaving you with the good stuff you get from him.