Husband newly obsessed with a girl from work

So a little insight... I dont think my husband would ever cheat and I love him very much. We have been together 7.5 years, married for 4.5. I'm currently pregnant with our second and we have a toddler. We haven't been having sex very much(I mean like once every 6-8 weeks...). We haven't spent very much "us" time since having our first child.

Recently he has started talking about this girl from work a lot more than usual and shes been texting him after work. I had found out that they went to lunch together, just the two of them, a few times. I told him I was uncomfortable with that and if they are going to do that someone else needs to go with them, not just the two of them. He understood where I was coming from and since has said someone else went with him. That was probably almost 2 months ago. I never look through his texts but something just told me to tonight and my fears are now worse. Apparently every day she texts him when its break time and it sounds like they are spending their breaks together. Still going to lunch just the two of them, with her discouraging him asking others to go. Him offering her rides places during the work day etc.

I know I shouldnt have looked. But now I just dont know what to do. I feel like if I say something he will either continue and hide it more or he wont. Theres not really much I feel like I can do. I dont know if this is stemming from us not spending one on one time together so hes looking for that from another female or if it's not even related but that's what I feel. Just looking for advice I guess before I talk to him or dont...