[Rouge]

As an experienced reciever, I'd say that you're still getting used to the relaxation involved. I'd take it very slow with moving yourself, and focus on staying relaxed as you move. Try having him stay still, then practise moving yourself on him while keeping yourself relaxed.

As far as pushing him out, a hard penis is very hard to push out of any hole without moving the body. He must be pulling back a little when he feels you tighten, or he may be soft, or perhaps you're moving and don't realize it. You're more likely to cut off his circulation than you are to push him out.

Try this: have him lay on his back while you control the penetration by lowering yourself onto his cock. Your whole body will be tensed as you are holding your body weight, and you'll be able to practise relaxation and test your movement capabilities.