Yes, of course you're risking losing your friendship. You're obviously pretty young and if you do start a relationship then, face it, it's not going to last forever.

However, if you don't go for it you'll spend the rest of your love life, happy or not, with that thought chiselling away at the back of your mind. "Would it have been better with her?"

So yeah, it's a mistake, without a doubt. But life is mistakes and this is one of those that you have to make. You're at least half-guaranteed some pretty good times out of the deal.