At the beginning of a sexual relationship, you tend to have sex pretty much any time you see each other and you've got more than 10 minutes of privacy. (You do, right? I probably shouldn't be using the presumptive "you." I do, anyway.) Some of it is the thrill of a new relationship, but some of it is that feeling that you haven't had this kind of sex in a while and maybe you won't get so many chances to do it, so you better grab when you can. It's sex that's partly based on wanting to have sex, and partly based on fear of not having sex.
And then comes the point when you're comfortable coming over, having plenty of time and privacy, and you share some dinner and talk a bit and hug a bit and go home. It's easy for this to feel like you're getting desexualized, domesticated, like the lust and passion are dying. But I don't think it's necessarily so. A little bit is the loss of that initial flame, but it's also the loss of that initial desperation, that worry that "I could lose this at any moment, gotta get while the getting's good." Having someone you can fuck, and not fucking them, can be an act not of passivity but of fearlessness.
Fucking like there's no tomorrow can be awesome. But there's great comfort and strength in the way you can live when you believe there is a tomorrow.
(Also: Hi JM's mom! I hope you are feeling better soon! Stay strong!)