For your first question (and throughout), you talk about how much men enjoy sex. Which is true, however...

I think the question is wrong to get the real answer about why men enjoy sex. The question shouldn't be, "What does sex feel like for you to want to do it so much?"

The question should be, "What does a lack of sex feel like to make you want it so much?"

Because, in psychology, we learn that people run away from displeasure and towards pleasure.

The lack of sex – even after just a couple of days – causes a number of increasingly painful psychological side effects. Self esteem lowers tremendously. "I'm obviously hideous. I'm not enough for her."

It makes me question whether or not she's still in love with me. It makes me paranoid, wondering if I did something to anger her or make her disappointed in me.

I become much more easily agitated and grumpy. I start feeling depressed. All I can think about when trying to work or do chores is how much I want her naked body next to mine. It takes over my brain.

Yes, all of this EVEN IF I know we both have very busy schedules. It's illogical and makes no sense at all, but that's how emotions are. What comes with age and experience is the maturity to not act out every feeling you have. That doesn't mean you don't feel these things. You just push them down enough so you don't act them out externally.

Actual PIV sex, however, isn't the only cure for this (for me, anyway). Any kind of very intimate act can have me waking up the next day feeling refreshed. One of my favorite things to do when neither of us has the energy to have actual sex is to sit up in our bed, put a pillow in my lap, and have her lean back on me topless. We watch one of our shows while I touch her – rub her head, caress her cheek and neck, massage her upper chest, and hold her boobs. She usually falls asleep, and I am in heaven.