What do we do now???

i have lived next door to be best friends scince we were born{13 years}. i practally live at her house its my second home and her family is my second family. her brothers are like my brother. but lately i have been getting very close with one of the brothers. we have always called eachother babe has a joke but now were saying it alot more often. last week i was sitting on the couch and he jumped on me and said watchya watching...can i sit with you. he sat down next to me and we ended up falling asleep on eachother that night. then last night we were sitting in the hot tub talking and then there was an okward scilence. then he scooted closer to me and we kissed...more like made out.also this week my bestfriend went on vacation so i hung out with her brother a lot.and now insted of just saying good bye we kiss eachother good bye.and last week at the mall i saw him and he litterally jumped on me and we started makingout in the mall.i love him but i dont want to hurt my bff waht do i do???