As others have mentioned, you need to ask her. Could be any number of reasons. One thing comes to mind, however, as it's been known to happen. Some women initially believe they can handle a relationship with a crossdresser, and then later realize they can't.

Why not ask her instead of us who don't even know her? Even if we would know her, the only true reason is what she could only know, right? You're still so young.. You'll find someone again. Perhaps life just needs to give you some important lifelessons, to learn love, that it comes along with responsibilities, trust,... Who knows. Only time can tell.

you borrowed her dress?

You looked better in the skirt?

You looked better in makeup than she did?

That's what girls do if you don't dump them first. Girls are mean.

she's a man now after dating you

You didn't make her happy.

Maybe she tried to be supportive of you but didn’t quite understand you. Some things don’t always work out I suppose. Some people want different things in life but I wish you nothing but happiness 😊

Because your a dude who dressed like a chick and she needs someone who is more masculine maybe?

Didn't she tell you?

Who knows ask her

Because you wouldn't stay in the kitchen