Sex with the ex

My boyfriend recently, mentions to me that he had sex with his ex-girlfriend twice( the night before and the day after). We have not had sex in a year because he's occupied at work. I'm hurting right now because I never starved him when it comes to sex. I warned him several times about that same ex because a couple of months ago he was out of town, I called him and a lady picks and I got to find out she was one and she told me that she is coming for her man back. And he drops this bomb on me, I'm so confused. I need help because I don't know what to do.