Am I going crazy

I had a little girl 7 weeks ago and have felt very off with my partner I’ve thought he’s been talking to other people and it wouldn’t be the first time. He accidentally left his spare phone at home this morning and i would never usually even look but i did and he had an inbox from a girl on Instagram. I couldn’t read it or he would see its been opened. I looked at his snapchat and he had sent chat messages to a few girls on there too!! I feel like I’m going crazy i know if I confront him he will know ive looked. I don’t know what to do as i want him to leave now ive seen that! But i feel bad for looking! HELP