Most Helpful Girl
Yes, he cheated. His feelings for her are irrelevant. You SHOULD be worried.
Ugly truth right here, I'm more worried about you than I am about him. If you cannot even see how what he did was blatant cheating, then how can you ever demand respect in a relationship? Your reaction to this told him that what he did was perfectly OK, and he will definitely do it again now that he knows he can get you back afterward.
If you're ever questioning a situation like this, then reverse roles for a second. Think about how HE would've reacted if you got into that same fight, didn't break up, he sat at home upset about it, and you went and made out with a different guy multiple times. Think he'd question whether it was cheating or not? Think he'd forgive you? Think he'd take you back? Probably not.