How to Deal With Bipolar Bf?

So, I actually don't know if he's bipolar or not, but I HEAVILY suspect it. I know that his mom has the same type of disability, even if its not bipolar, maybe personality disorder or something of a such, but I know that a lot of them are hereditary and I've noticed that he feels amazing for 2-5 days and then, with no explanation, or me saying something that I wouldn't think is a big deal, he switches off and he feels terrible, insecure, and unloved for 2-4 days. I don't think that Ive been a bad girlfriend, I try not to tell him about my problems or my worries because I don't want him to suddenly be in a bad mood, but I never know what would set him off. I don't know whether I should mention it to him, or just try dealing with his mood swings, because it's not his fault, but I also have to take care of myself, and I feel like Im walking on eggshells while talking to him.