Oh, dear God. Don’t “dump” her because you decide to frum out. Dump her? Seriously? You dump a tramp. You don’t dump someone you love. You can end things with her, without you dumping her.
Merely explain that at this point in life you must go your separate ways. Once you do so, completely cutoff any and all contact. This means deleting her from facebook, no e-mails, calls, texts, etc. Do your best to forget about her.
I’m not sure I support any of this, but hatzlacha to the two of you.