I want a woman to put me in chastity and coerce me into becoming more and more of a cumslut. Ideally a classy lady who doesn't get involved with the sexual aspect but simply finds it entertaining that I'm being converted into her obedient faggot.
I suspect the best way to get a taste of this idea is to give my chastity key to a prostitute/dominatrix and devise some role play around it. Could easily take it up a notch from there!
To be honest, I think most of my fantasies are centred around a dominant woman. But I have dreamt about simply being chucked in the back of some guy's van and abducted as a gay sex slave - castrated, pozed, then eventually released - and never able to look at women the same way.