Bf replying to casual encounter ads?

So my bf of 7 years, father of my child was replying to Craigslist ads on the casual encounter section. Some of the headings said "no strings attached" and "looking for fun". Now these were from this past fall but I just found them today as I was trying to find an old email he needed. We were still together when he replied to them. He said things between us were not "good". I wasn't awAre they were not good. I'm so hurt. What would you do?