monstermonstre:

if you’re starting a sexual relationship with someone, i suggest you do the “no sex tonight no justification no apologies” test early on

say one night you’re kissing and cuddling and you see things are headed towards sex and you don’t feel like it because of any reason at all, just say something like “i’d rather we just cuddle” or “not tonight” or anything really but the important part is that you offer no justification (”i have my period/a headache/i’m tired”) nor apologies (“i’m sorry”).
just “no”, in whatever form it takes, while forbidding yourself from giving a reason why or an apology. because you shouldn’t have to do either to have the right to refuse to have sex with anyone, even someone you’re dating.

and then see how they react

if they try to change your mind or pressure you or act offended, don’t date them.

(and if you’re someone who would feel offended and/or want to try to change the mind of someone who’s dating you and refuses to have sex one night “just because”, then think long and hard about the implications of that behaviour, educate yourself, and don’t date anyone until you’re done growing up)