lol, dude, dont' tell her you're breaking up to become a pick up artist, are you kidding me? Think about it "hey, sorry, I'm breaking up to become DJ/PUA" her: "f u as***le" she calls all her friends and tells them this is why you broke up with her. Word spreads and now everyone starts hearing how you dumped that girl so you can be a PUA, then you go try to "pick up" some chicks, and they know that you're just in it for the "pick up", how do you think that will go over?
Common, be smart man. Don't tell her ANYTHING about DJ stuff, PUA stuff or ANY of this!! You can't be giving away your power! Never tell people that you are learning this stuff cause most of them will use that against you and it may come back to bite you in the butt. Keep your styding and knowledge as your own personal tool, no need to tell people about it, it will be counter productive. If everyone knows, then every move you do or every thing you say they will start trying to figure out what you're really up to and if that's also part of your "routine". Trust me, you don't want all of that. Keep this site and anything else you learn to your self, and keep improving but do NOT talk about studying this stuff.
With the girl, you don't need to tell her the ENTIRE truth man. Just tell her "hey, I loved spending time with you and all, but this is not working out anymore, sorry"