I did quite a bit of "swinging" in my single days and indulged in mfm fun with 6 different couples, 3 of them on a repeat basis. I was 19 the first time I fucked another man's wife while he watched. They were in their mid-30's and I thought they were an "older" couple at the time. She was a very sexy woman who loved to fuck. Her husband was average in size and she had a thing for bigger cock. He liked watching her and jacking off. I was nervous as hell the first time I fucked her, but they were experienced and showed me the ropes. I found that I really got off on having the husband watch me bring out the slut in his wife with my big cock. Through them, I met another couple, and was on my way. Discovered early that there are a surprising number of couples out there looking for bigger cock for the wife.
I have only done pussy/anal dp with one couple. Due to my size, most women won't allow me near their ass with my cock. But I used to get together with this couple on semi-regular basis, and the wife loved to have her pussy and ass fucked at the same time. Her husband was on the small side (probably about 5"). He of course got her ass and I her pussy. I was a little weirded out the first time we did it. I was experienced at mfm by that time, but it consisted of one guy fucking pussy while the other got sucked, tag teaming, or taking turns getting sucked. Watching how turned on Linda got with her husband and I inside her at the same time was amazing. To this day I have never seen a woman enjoy fucking with such abandon. She would cum SO DAMN HARD. I can still hear the grunts, moaning, whimpering, screaming, dirty talk. Her husband and I never lasted more than a couple of minutes when double fucking her, but that's all it took to get her off big time.