I would talk to him about it. My best friend was going through a lot a few years back and we were texting all hours of the day and night, over the xmas holiday and I spent several nights crashing at hers to make sure she was okay. I openly talked about it with my wife. Because we were so open, there were never any fights about it and she was very understanding. She knows my best friend quite well and knew we were only friends, but I'm sure if I wouldn't've talked about it that it could've made for some unpleasant thoughts from her and awful needless arguments. If they are just friends, then he should be able to be open about it. Letting you know who he is talking to is a start; he may not realise he needs to say more.
YAY! I'm now 12 weeks and have my scan in 4 hours!