So hes bi. my best friend is gay. and im straight?

my friends and I have been friends since elementary school. Were in highschool now. My friend Isaac is gay and has never had a boyfriend, until now because he's dating our friend Stephan who happens to be a biual. Well ive liked Stephan for a while before Isaac has. But Isaac was the first to "claim" him I guess and I never said anything to get in the way. Right now Im not sure if I should just move on& forget about Stephan... or hope for a chance? Because Stephan has been telling me that he and Isaac have been argueing so much lately and beginning to have doubts. Soo yeah, what do you think i should do?