Fiancé flirted and chatted with girl who'll be at our family party

There's an Overnight beach party and I'm seven months pregnant I rather stay home and rest than go .   my fiancé still wants to go even if I don't but the problem is that part of his friends and family is a friend of the family that he has a crush on and tried to contact and video chatted with her while we were together and the conversation was very flirty and he wanted to see pics of her. I forgave that two months ago. I read all thT myself on the iPad.        would you let him go knowing she'll be there and it's an over night thing?