My wife and her boyfriend (who's also her highschool sweetheart) have been together for 6 years (her and I have been married 14 years). The one and ONLY time I joined them for a 3Some (last year), he was totally awkward and insecure. Ironically, whenever it's just him and my wife, he's take charge, a bit rough and even "agressive", which my wife loves. He's also fine with the 3 of us occasionally hanging out in public together.
If he only fully realized the awesome sex/love making my wife and I have partially due to the amazing sex she has with him... Or that she keeps me locked in my cock cage and takes the keys with her whenever she's with him, I don't think he would have been nearly as awkward during that one and only time.