Sort of cheating?

I caught my SO talking to another woman, again. We've been together over 2 and a half years, and have been together since we were 15. We currently live together, and he's done this once before. He never actually gets to the point of doing more then just talking though, because he is shy-ish. At what point do I need to leave the relationship? And how would one even do that when they are living with their SO? I don't even know if this qualifies as cheating or deserves a break up. I need help. Please and thank you.