Positives?

I don't want the negatives. I already no them. But are there any positives to a 3 sum? My husband has been asking for one. I finally told him if we can find a girl i like I'll do it once. I have laid down some ground rules. But I'm still kind of nervous. I no it could cause us to break up. Or cause cheating. I have enough trust in my marriage for that not to happen. Just want some positive insight. Thanks