What should I do?!

Basically, I was with my boyfriend for like 2 years and we split up for like 2 months last summer. We then got back together again and been together ever since. I’m

Now 37 weeks pregnant and we live together.

Basically he told me his password yesterday and whilst he’s in work this morning I’ve got on his Instagram and read a message with one of his friends from when we wasn’t together saying he shags like 3 birds a week due to him having a different accent and he’s killing it here with the girls. But when we spoke about what we had done since we hadn’t been together he said he just kissed another girl. I don’t know wether to question him or not because he doesn’t know I’ve been on his Instagram