I'm going to tell my bf he needs to lose weight or I'll break up with him
Thats harsh. Why force him to lose weight?
I'm getting tired of his arm flab flopping all over the place, it's getting pretty annoying
If your bf's weight is becoming too much of a problem and he doesn't want to solve it, it's ok to leave them. However, do not expect too much from them as losing weight is somewhat of a lengthy process. Keep things realistic.
That's fine, I have checked out other guys at work and if I find one I like better I will cheat on him.
Thats a bad attitude to take on the whole thing. Do they mean that little to you that you're looking for someone to cheat on them with? Just break up with them and save them the heartache if you're already looking for someone else.