Okay girl cutting is not cool, not okay and won't make you feel better, over all you will just end up with more scars, get some professional help.
Seriously, how do you think it will be if this doesn't work out, how will you feel then what will you do, I am not trying to be mean at all,( My brother is Bi-polar/Manic Depressive) but if you have depression something like a bad relatinship will/may set you off.

I think it is awesome that a) you met someone and b.) you are confident enough to say no when you don't want to do something

You need to stay in touch with someone like a Doctor who has you in confidence and won't judge you etc, for the depression and tell them asap about cutting, you are 15 if you get on this now it can be stopped or kept to a minimum, if my brother had known at 15 he would not be as sick as he is today, he wouldn't be cured but he would have half the pain and suffering that he has now because it went untreated. I couldn't help my brother because I was too young but you i can try to help, encourage you to get professional help. And I am not trying to make this about me I am just using the experience I have had to try to let you know that it is okay to be you, but you don't have to suffer alone. And they can stop cutting, and further help with your depression.

I hope you aren't mad, I am glad you came here to ask and i hope everything works out for you.

Oh and every girls dad flips out i would guess in their own way..they mean well, they worry that's all.