boyfriend & his best friend

so my boyfriend and i have been fighting for the past 3 weeks. he started it because he wants to go to college and doesn’t think we could handle the distance. so we broke up but we still talked a little bit. for 2 weeks i found a bunch of stuff out from his best friend and i found out that he lied to me about a few things. i’ve been with this boy for 3 years on and off. i know it’s not healthy but it’s just so hard to let go because we have such good days and i love him. anyways, now he wants me back but i’ve been talking to his best friend & we have been flirting back and forth. last night i hungout with his friend and we hooked up... we both agreed to not tell him but i feel so bad and i def like his friend, but i also don’t think i could have a relationship with him. and i def wanna hangout with him again too lol. can i have some advice? like has this happened to anyone else lol??