In my experience (29F), it is nearly impossible to sleep with someone and not catch feelings. It's natural that when you give someone your sexual energy, you get drawn more and more to them. You're young. I would break things off and take it as a lesson. Never sleep with a girl who has a boyfriend. It is rare that they will ever break up with the boyfriend for you, and even if they do, they may cheat on you with their next one. It's not anything against her, but she clearly does not have strong morals to have sex with you and then say, oh I still want to marry this other guy. To her, you are just someone concenient while she is away from her man.
In my experience (29F), it is nearly impossible to sleep with someone and not catch feelings. It's natural that when you give someone your sexual energy, you get drawn more and more to them. You're young. I would break things off and take it as a lesson. Never sleep with a girl who has a boyfriend. It is rare that they will ever break up with the boyfriend for you, and even if they do, they may cheat on you with their next one. It's not anything against her, but she clearly does not have strong morals to have sex with you and then say, oh I still want to marry this other guy. To her, you are just someone concenient while she is away from her man.
If small things like this are already a problem, you both should separate.