I have tried various BDSM sessions but I am too much of a gentle soul. My inner bitch is buried very deep inside me.
Cuckholding usually means the guy wants to watch you with someone else, usually wants to be "forced" to watch. He wants to be made to sit in a chair, possibly tied up, and be told how much better the guy you are fucking is than he is, how great the guy's member is compared to his puny one, etc. Sometimes these cuckhold fantasies include the guy who's being cuckholded being "forced" to do something with the other guy (ie. suck his dick or lick his ass).
Personally I can't do it. I like one on one and am more loving and affectionate than a real bdsm session would call for.