I can't believe I'm falling head over heels for this girl.
Oh wow, why are you so attracted to her?
She's a sex buddy I've had for a while from Switzerland but I'm starting to want it to be more than that.
She must be very attractive, but don't rush into the relationship. Take the time to know her as more than a sexual partner.
While I like her it's not like I want to marry her or anything. I still prefer to keep the sexual side right now.
If that's how you feel then yeah, you shouldn't rush into telling her your feelings or anything like that. Since you were sex buddies, she likely wasn't looking for more than that either and you might scare her off with things being more serious. If you get to a point where you feel you would value a relationship more than sex though you should at least tell her.