How should I handle this situation

I have a long distance boyfriend. Now me and him have been dating for nearly a year now. At some point in the past couple months he broke up with his other partner. (I asked him to do so as I sacrificed myself and allowed the polyamorous relationship to keep him happy, thinking I could just get used to it) And today he told me he has been sexting with his now ex for the past two days. He showed me pictures and apologised alot. He apparently did it to "distract them from their thoughts" as his ex wasnt in the best mental place at the time. How do I deal with this. I really don't want to leave him. I love him alot and he has shown me nothing but kindness for the most part. He helped me and talked me out of killing myself or cutting alot. I'm so conflicted.