Boyfriend flirting with manager?

My boyfriend and I work at the same place. We broke up a few weeks ago for about a week. I recently found out that during that week him and my manager were texing a lot and he was telling her how sexy she was. I feel so hurt and I feel embarrassed going to work. Am I wrong for feeling this way even though we were broken up? I figured if he was going to talk to someone it could at least be with someone outside of work. I can't believe my manager would do that to me.