It's erotic to watch a guy cum while fucking. The body shudders, thighs quiver, dimples in the butt cheeks, balls twitch. And erotic to know what the cock is doing inside that hole!
The guy who popped my anal cherry (I was in my 50's, and he was thick, and yes, IT HURT) - he told me about "silky seconds" and how even a thick erection goes into your freshly-spermed hole without much discomfort.
Cum deep inside and don't pull out!