Stuck between choices

Saturday I'll be 32 weeks (8 months) pregnant. This past weekend, my SO and I had a spat bc I saw that some girl sent naked pics to his phone. Multiple messages were sent between them two, one him asking if she wanted to have a threesome and another he asking "you not tryna f**k". My heart was literally torn to pieces because I don't know what to do. We talked about but I feel like I can't trust him but I don't want to raise our little girl as a single mom. I'm torn between benig a family and leaving to further protect my feelings. I've suggested we attend counseling to figure out the reason behind this (this isn't the first time I've seen him messaging girls). Any advice? No bashing please.