I need serious help with a relationship question

ok so i have this girl named brittany who was my g/f for 3 years and we loved each very much but then one day she let some other guy kiss her and she has lied 2 me a view times and so we broke up but we both still love each other very much and have our whole future planed out with each other and rite now we r kinda half dating only b/c on the other side i have a bestfriend named sydney who i met the same time i met syd and me and brittany started dating before me and syd even had a chance but me and syd stayed very close friends and now i think i like her alot and everyone always says that me and her would make a good couple but i dont kno wat 2 do b/c i love brittany and all and we already have our future planed out but for some reason i cant stop liking syd and i know she likes me 2 and i want 2 also be with her but i dont kno which one, wat do u guys think? any advice?