Is this normal or am i evil?

Ok so im a 19 year old recovering addict. Last year (on my 18th birthday in fact) i become friends with a girl whos 2 and a half years younger than me and clean (well shes an ocaisonal stoner). Over the past year we've spoken loads and after a few months of knowing her i started feeling as if i have a bond with her and that i could show her a side of me that i cant show to anyone else.

After a while she said she likes me too and we kinda grew closer and closer. We've kinda been in an 'informal' relationship, becuase both of us cant really be in a full on relationship at the moment cos of her depression and family issues and my addiction/recovery.

But heres the weird part: despite the fact that i feel as if i love her ive constantly felt guilty about it cos she was 15 when we met and even though shes 16 now and its not technically illegal (we're in the uk) i still think i might be in the wrong somehow.

I suffered sexual abuse as a kid and i know it fucks people up for life (i was a crack addict at 16 lol) and i would never want to put another person through that.

But last night me and this girl were talking on the phone and she brought up the topic of sex and then said she wanted to have sex with me. Im kinda sexually awkward and as an ex opiate and other drugs user, i dont have much of a sex drive and can rarely have orgasms. And i can honestly say that before last night, i had never once considered doing anything sexual to her. But then when she said it i thought about it (and havent stopped since) the idea at first kinda shocked me more than anything. And now i kinda like the idea and im not sure if that makes me some kind of pervert or something.

I feel closer to this girl than i have with anyone else ever so i kinda think sex with her would be less awkward than with other people. But at the same time i feel really bad for thinking that way cos shes younger than me and she was only 15 when we met so in a way i feel as if im im the wrong and although its not what id call abusive im still worried that it might make me just as bad as people that do abuse people.

so like in short is thw fact that i liked the idea of sex with this girl normal? Or does it make me a pervert? And what is the right thing to do here?