it's normal to panic - sounds like you have a lot of mixed emotions right now. Leed is right in that fooling around can be dangerous - consider what YOU want out of all of this - and be careful that the friend is just not taking advantage of you. (they might know that you like them and just want to take advantage of that fact - they don't seem to seriously care about how you feel etc) From this specific post you don't seem super excited or anything about that/into the friend so it doesn't sound healthy to me.

as far as 5 years younger - I don't know how old you are and that does make a difference to me. Crushes happen - sometimes they're not always good to follow up on but there's no SHAME that you fall for someone. Emotions aren't always controlled. But you do have to be careful what you do with them - again, what's healthy for you and the other person? Just think about it, I think you'll find the answers if you be honest with yourself