Should I get even?

[Connor]

So a friend of mine, well ex-friend now, told the girl I like bad things about me. He told her things that I didn't want him to tell anyone, especially her. Yesterday, I tried talking to her and she immediately brought up the stuff he told her, and she hates me now. I was going to go in the same prom group as her, but now I can't. He did it intentionally too, I just can't figure out why.

My hypothesis: He likes the girl too. I was about to get into a relationship with this girl last January, but she randomly became uninterested. I'm thinking now that my friend has been feeding her bad things about me for a long time, since they are really close friends. Another reason I think that is because when I texted her yesterday to ask when he had told her those things, and she refused to tell me.

I'm pretty mad, but I feel even more hurt and betrayed.

Now I'm just trying to decide if I should retaliate. I'm good at this stuff, I mean I'm creative enough and I won't feel any regret about completely fucking this kids life over. I know it's morally wrong, but I really want to ruin what he's ruined for me. Please don't say "Be the bigger man", give me a real reason of why I shouldn't get back at him?
I'm not trying to win her back, my reputation with her is ruined. I wouldn't even ask her if she wanted me to just because of he she'd look at me. He didn't tell her that I cheated on a math test, or something small, he told her I drink, smoke weed, and tried to hook-up with a slutty girl. (She tried to hook-up with me, oh and the slutty girl is also this kids best friend...)