My best friend (who at this point I should explain is male, and a single father) and my sister have just admitted to me that, having grown closer over the last few months, this week they "sort of kind of became a couple", and that they weren't sure how I'd feel about that.
Now that they've told me, and I have utterly failed to bite their heads off, they seem a lot more relaxed. We're going to get together tomorrow and see what we feel like doing.
The only potential problem I can see with this is that both of them have a tendency to tell me about their respective sex lives, and I really desperately don't want to end up with loyalty issues, confidentiality issues, or downright "ew" issues concerning either of them.
On the positive side, at last he has a girlfriend, and she has a boyfriend, that I can completely approve of!