To those who have felt that sex outside/before marriage is worthless, please share your opinions on what have you realised about it?

Hi I am an new adult, and i feel sex is an incredibly intimate and sort of a sacred thing we can do with someone, i feel that if we do engage in even well meaning and deeply intimate sex with someone, and later on don't marry them, then our ability to be intimate with the person we actually do end up marrying will surely diminish, even if slightly. But I want a more in depth explanation, maybe just a bit more elaborate than what i have felt. Just see me as your younger sister 🤗 and tell me what you would like to. Be open and direct. I just want the truth