Hmmmmm…it sounds a lot like Belial to me as well. In my experience with him, he will test you and see how far he can go with you and what you allow, whether that is sexually, magickally, financially etc,. The fact that you say you are normally so much about control, might mean that your darkside wants someone else to take the reigns a bit, so that you can rest in a way. Belial is all too happy to oblige in that apparently.
Never forget that your body is your own, and if things are getting too much and you REALLY want to stop it, tell him that and make sure you’re getting something in return for your services to him( as Lady Eva suggested) as he is taking your sexual energy( with your consent) and therefore ask yourself what am I getting besides pleasure from this, and is it enough or an even exchange? Perhaps you can ask in return help with things in your life/personality that you’d like to change?
If this entity, no matter what it is, doesn’t respect your boundaries that you are setting,(though in my experience Belial would) and you truly want to disconnect with it, I’d suggest throwing away your toys( as they are full of it’s essence and help establish that connection to you) and if you can, remember one of the times this being had it’s way with you and then in your mind make a picture of it( like you are watching yourself playing with your toys on a t.v. screen) then shrink the picture smaller and smaller until that memory is a tiny speck in your mind.
Then visualize/imagine there’s a chord attached to it and you, sever the chord with an imaginary knife or sword, and then command that the entity and it’s power over you is gone and banished from you forever as you watch it shrink down to nothing and dissapper . That should help get the entity and it’s power over you, out of your life if you need to do so.
You said that you are strong spiritually, therefore if you have a god or goddess that you pray to, I suggest that you do so and tell them to cleanse and purify your home and body from this being’s energies as well as take a salt bath and burn a cleansing incense like sage in your home (especially in the room/rooms this being has had it’s way with you!)
Good luck, be strong, and have fun \m/