I’m so stupid 😭

I’ve been in a spat for a few months with my other half after he messaged another lass and attempted to meet her. I haven’t been able to get over this. He swears he’s sorry and it will never happen again etc etc. But I’ve just worked out that in March 2020 he was messaging a lass and I got sent screenshots, then again in October he did the same and then again in December. 😭 I’m currently pregnant with his child. Why can’t I find the guts to leave this man and why do i keep letting him do it to me 😭 I’m so stupid 😭