I don't know what I feel about your post. On the one hand your boyfriend's anxiety bugs you and that's okay but there's a hint that some of its degree is predicated on you might like to start something with the T.A. but I had to laugh that you built so much into his looking at you and smiling. Uh, that's what they have to do in class? They look out and smile at students, especially pretty girls if they're guys. They want good feedback that you're getting it and you're probably grinning at him :-)

I'd treat the T.A. thing as if it were a 13 year old's crush; you don't know if he has girlfriend or what his circumstances are and I don't hear any need for new angst in your life right this minute?

I'd either split with the boyfriend or try to mend the harsh things it sounds like you said the other day. I figure I have enough of my own mental health problems that I try not to spill on my husband and his. Unfortunately, mine spill over and I correct him and let him know what is wrong with him, even though that's not my job. As he often has to point out to me, we're on the "same team" so I'm supposed to be helping him with his, not aggrevating them by pointing out what he can't do anything about on his own.

My advice boils down to deal with one guy/relationship at a time. Clean up the boyfriend relationship so it continues or ends "pleasantly" and then go on to the next step. I can't tell from your post whether I feel you are being driven away from your boyfriend by his behavior or whether you are using his behavior as an excuse to stray because you are bored or unhappy or unwary with yourself and previous habits? I would stick for a bit and see what I could do with the boyfriend and myself in relation to the boyfriend. You've identified several areas of possibility/question in the relationship and I'd look at the ones that might have to do with you directly, if you have trouble "sticking" then you'll know more about yourself than if you just say, "it's him" and move on?