Hi I dont think u should tell him now, cause he probably wont considirate have something serious causr u r with his friend, what I think u should do is break up with ur boyfriend cause u gonna hurt him more later if u stay with someone u r not in love with, break up and give urself time, if this guy like u and u still like him after all u could maybe go out like friends and get to know eachother, but dont try break his friendship (probably anyway could happend), and dont cheat or go on dates with his friend cause that would no go anywhere good, if u break up, give urself a lil time, and if after all u keep loving him then try that he notice u, after that if he wanna be ur ex boyfriebd friend just tell him to tell ur ex that he likes u before anithing happend so it wont look that bad, and u can live peacefull...
Be sure of who u love, and dont make nothing that would make u look bad or something that would hurt ur bf, and dont worry everithing is gonna be ok when u do things right way, xoxo