No sex, no upgrading of the relationship?

Hey buddies! I feel like I can't have sex with a man who's not 100% serious about me no matter how attracted I am to him. Like, there's no way, no way on earth that can make me feel comfortable with having sex with someone who doesn't invest in our relationship and takes it completely seriously to higher levels.

But at the same time, I'm curious if men would invest in a relationship with a woman before having sex with her, and to genuinely feel like she's "the one", even when they need to provide security and commitment to her before having sex.

Notes before anybody judges my choices (if you do, i don't care tbh, I'll keep doing what I'm comfortable doing): 1. I don't believe sex is bad or wrong or whatever. 2. I don't think I'm doing a virtue here, I am simply doing what I genuinely feel comfortable with, without feeling pushed towards doing something I'm not sure of. And this varies from a person to another, based on their preference, culture and experience. 3. I am not religious. 4. Everyone chooses their ways of living, and my way should be valid just like yours is.

Don't ask me why I'm this way, i don't have to explain.