What do you guys think?

Me and my husband are separated. Yesterday we met up to go to my doctors appt together for the baby.

I saw he texted a girl “Sarah.” I didn’t say anything then. I looked at the messages later and it seemed like they spoke on the phone before and he said to her “just thought about you.” I then asked this morning and he said she was a family member.

My mind is telling me it’s someone new and not to be dumb. Just seeking some advice or guidance? Thanks