What do I do?

I have been in a relationship with my partner for a year and 6 months. Due to lockdown, we only saw each other once or twice every two weeks. Our relationship was good and spoke over the phone all the time. These past 4 months we started fighting a lot, he got a new group of friends and started partying/ drinking a lot. I may have told him that he was turning into an alcoholic and obviously he did not react well to that. Our fights became worse and I started feeling insecure. Last week Monday I found out that he took another girl out for coffee the previous Friday, they had been flirting on Instagram. I confronted him about this and he apologised and says he needed someone to talk to. He has been talking to another lady as well and telling her about our relationship problems, I believe this lady was becoming something more to him. He has been apologizing to me and wants our relationship to work. I don’t know what to do, he really broke my trust. I feel like a failure in this relationship and my insecurities have become so bad. Am I so bad that he needed comfort elsewhere?