The guy i like has a girlfriend...what do i do?

I really really like this guy named henry and weve been getting closer over the past couple of months and we were at a party and he asked me to snowball and we danced together the rest of the song, but the next day he started going out with a blonde. Theyve only been going out for a week amd theyve gone out in the past and broke up for one reason or another but either way i really like him and id do almlst anything it takes to have a relationship with him and the girl and i were sorta friends but we havent been talking since they started dating even though we all go to the same school. I just dont know what to do and i really want to be with him