Are Ты serious? That's wrong on so many levels. You're gonna just break up with your boyfriend just because somebody else asked Ты out. That's messed up. Ты figure out what Ты need to do. I'm not helping Ты 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 Ты even consider what it'd do to their friendship. Gosh if I were him I'd end it with Ты here and now!
Have Ты 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 Ты happy with Dom? If Ты have to even ask this question, I doubt your relationship with Dom is very strong.
But only Ты can answer this question. Think about how each boy means to you. Good luck.
Also, I would recomend asking for Совет at link Далее time. People at this spot tend to be a bit harsh. ;]