It is a universal truth that twinky guys with girlfriends are never completely safe from the possibility of having their face rammed into the pillows by a bigger, bulkier man, at the behest of said girlfriends.
As a result, if you are one such twink, it's important to figure out where you stand on the very real issue, so you can enact an action plan in the event of a real emergency. I would recommend imagery exercises, to prepare your heart for the shock of the real situation. Try engaging in masturbation, while mentally bouncing in his lap, legs wrapped around his back, his arms bear hugging you, locked into skin-to-skin contact, his tongue invading your passive mouth. Whilst your girlfriend stands just to the side, stroking your hair, complimenting you on doing such a good job for her, for being such a good girl.
Of course, with no training, any given twink's brain is at risk of shutting down in such a situation, but after successive months of image training, you will be able to remain completely present and aware in such situations.