I've been in several LTRs ranging from months to years. It's true the sex changes, but I wouldn't describe the sex as fizzling out in my experience.
The excitement you feel (as a man) during sex in the beginning is all wrapped up in the conquest and the thrill of new pussy. It feels great and exciting (I fucked a new girl a few days ago and I'm still relishing how it felt to slide into her wet pussy), but in my experience at least, the early sex, although good/great, has never been the "best sex" of the relationship -- if the relationship turns into an LTR.
Later in an LTR the sex really does become an emotional bonding event (or it should). If you are not open/available to bond with the girl you are cumming inside of in a LTR, then you aren't actually in an LTR, you are just FWB (Friends With Benefits). Although I would still wonder about the girl secretly harboring feelings for you if you are in fact regularly filling her pussy full of fresh cum.
The excitement you feel (as a man) during sex in the beginning is all wrapped up in the conquest and the thrill of new pussy. It feels great and exciting (I fucked a new girl a few days ago and I'm still relishing how it felt to slide into her wet pussy), but in my experience at least, the early sex, although good/great, has never been the "best sex" of the relationship -- if the relationship turns into an LTR.
Later in an LTR the sex really does become an emotional bonding event (or it should). If you are not open/available to bond with the girl you are cumming inside of in a LTR, then you aren't actually in an LTR, you are just FWB (Friends With Benefits). Although I would still wonder about the girl secretly harboring feelings for you if you are in fact regularly filling her pussy full of fresh cum.