A few notes on ejacuation as well, since your character is going to be doing a lot of it. For me, when it happens it's a kind of pleasant burning sensation. Not heat, but that kind of subtle almost itchy burn sensation I get when I urinate, except magnified a bit. There's a kind of thick feeling that's hard to explain but is pretty clearly the difference in viscosity of the fluid going through the urethra. Not a very sexy thing to decribe, perhaps, but you might find a way of describing it that's sexier.All I have to say is: men are really weird.
Also, there's a distinct sensation associated with getting an erection -- again, at least there is for me -- it's a feeling of weight and compression, perhaps some sense of warmth. Sometimes it happens more gently than others. When it's not gentle it's usually uncomfortable and requires shifting things around because my penis has gotten a kink in it. Sometimes arousal also causes my testicles to retract, and when that happens the most obvious sensation is all the hair brushing against things as the skin contracts. Same thing happens with temperature changes, anticipation, nervousness (sometimes) and occasionally with a shock.
Finally, the penile sensation for those kind of 'eye contact' moments can be anything from a simple twitch to a full-on uncoiling. It really can be like having a living thing in your pants that's moving around.
- from one of my critiquers on the new project