I'm In Love With My Brother and we are already intimate, What Should I Do?

Me and my younger brother have always been close, he's 18, I'm 20 and recently we've seen our relationship blossom.
I wish I were trolling, that what I'm about to tell you is a lie - but it's not, please don't judge me.

It's been this way for a month now, we'd always been typically close siblings but ever since he broke up with his girlfriend, I would comfort him and say "it's alright, you'll find someone perfect someday."
Last week we were in his room and I said those exact words, we looked into one anothers eyes and kissed.

It felt weird, he came onto me but I reciprocated and before long we were french kissing on his bed, he was touching my knee.

Then, of course, our parents returned and I felt wrong. Kind of gross, even.

I went back to my room and cried. The next day we were home alone and he kissed me again, things got out of hand and we were doing things to each other, then we made passionate love and reclined into one anothers arms.

It's been almost three days since we made love, we've been kissing and doing other things whenever we can and I can honestly say that we are in love.

We've been planning our future together, and I'm beginning to think I made a HUGE mistake - I love him, but I'm not sure if it's like that.

What should I do? I don't condone what I did at all, please don't mock me, he came on to me and I was silly enough to get blown away by it all.