Someone of opposite sex staying over night?

So my husband has a friend from the guard who is lesbian. I've only met her a couple of times and my husband told me that at one point, a long time ago, they thought about dating for a split second, but obviously she likes women. Well, I find it odd that he seems to talk to her and meet her for dinner or have her over only when I'm gone or out of town. He never really talks of her or invites her over when we are all home. My son and I have been in Arizona all week (we live in Iowa) and he said she was going to stop by our house on her way home from drill. Well he tells me this morning that she ended up not coming over until midnight and she still had another hour drive home so she stayed at our house in the guest room, but then he says they were up awhile talking about her relationship issues with her girlfriend. If they stayed up talking she could have been driving home during that time, right? Am I over thinking this? I'm just feel like I'm starting to get red flags because she never comes over unless I'm gone and he didn't tell me about any of his until this morning after the fact...Opinions?