My ex wife(who was also my Mistress)used to cam our B.D.S.M sessions on an adult dating site.We met and became friends with a local guy(a Master) on there and would cam and chat with him.One evening,without me knowing, She invited him to our house and when He arrived I was ordered by my Mistress to strip.Although He had seen me naked on cam I found it humiliating to be stood there naked (except for my cock cage and collar)in person.I was tied face down by my wrists and ankles bent over a table.The Master then had sex with my Mistress with Her humiliating me by saying things like 'He's much bigger than you'and 'He can last a lot longer than you' etc.When they had both had their orgasms my Mistress came over to me and shoved her dripping pussy in my face and ordered me to lick it clean.Once done She put her strap-on on and started to fuck me in the arse(She had used this before as well as dildos and butt plugs).The Master then shoved His cock in my mouth and told me to clean it and get it hard again.As She watched me sucking His cock my wife thought it funny and started laughing and calling me a 'sissy faggot'.Once I had got it hard He told my Mistress that He wanted to fuck my arse,so they swapped places and He gave my arse a good fucking.After He had cum in my arse I was released,cock cage removed and told to masturbate over the table whilst They watched.So I stood there cum dripping out of my arse masturbating(both laughing and making humiliating remarks at me) and when I had shot my load over the table,They ordered me to lick it all up.
Having His cock in my arse felt completely different to having the strap-on,dildos and butt pugs in there.It was warm and not cold like them for a start and seemed to move in and out differently,it was a great sensation.
We did it several more times with other Masters and She even once invited a Mistress over and also a Mistress and her male submissive.

I had an MMF 3 some a few years ago, and enjoyed it a lot. Me and the other guy (my fuck buddy, black, thick cock), started off sucking each others cocks, then he fucked me. The lady joined in then, and she sucked our cocks, and we took turns fucking her. Of course, we still sucked each others cocks too, and he fucked me agin.