Are 당신 serious? That's wrong on so many levels. You're gonna just break up with your boyfriend just because somebody else asked 당신 out. That's messed up. 당신 figure out what 당신 need to do. I'm not helping 당신 with your soap opera shit.
Umm no! What kind of girlfriend are you?! To been consider breaking up with a man for his own friend! that is so shallow and rude. Not only will it wreck your relationship with guy one but did 당신 even consider what it'd do to their friendship. Gosh if I were him I'd end it with 당신 here and now!
Have 당신 ever thought about breaking up with Dom before this? Was it because of other boys? What kind of person is Tyran and would he make a good boyfriend? (I'm going to assume not. What kind of person asks out their best friend's girlfriend?) Are 당신 happy with Dom? If 당신 have to even ask this question, I doubt your relationship with Dom is very strong.
But only 당신 can answer this question. Think about how each boy means to you. Good luck.
Also, I would recomend asking for 조언 at link 다음 time. People at this spot tend to be a bit harsh. ;]