Cumming & Orgasims

Im gonna go straight to the point, ive only came one time that i know of and that was about a year ago, i recall that i never felt it happening but how do you know if you’re about to cum? Me and my boyfriend have great sex but i could never finish. Ive also never experienced an orgasim but i dont wanna miss out. I wanna experience these kinds of things with him. Any tips?