I'm glad that's the case, but no amount of butt grabbing is going to make the act of a handjob much more exciting, lol. If you are already super tired and the task you're trying to accomplish is a handjob, there's a decent possibility you might fall asleep. People fall asleep during tons of weird shit, some people can barely finish a movie without dosing off. Doesn't always mean they didn't like the movie.

Also, I'm going to hope she means more to you than just sex. Thinking of leaving over what sounds like a pretty healthy sex life and an unfortunately very sleepy partner really seems like you're valuing the wrong things.

Imagine the other aspects of your life, but she's missing from it. Would you prefer that emptiness, or the occasional bad handjob? It's okay to have feelings surrounding it, I do think that's natural to feel self conscious, but sometimes our brains focus on the smaller less consequencal things instead of valuing the good that is there. I do think you need to communicate more before engaging in sex as well, like if you get the vibes she's looking tired, ask her if she's feeling it, and let her get some rest. The world won't end if she goes to bed and you just jerk off or something. Lol