I hate to break this to you sweetie, but neither one of them are your boyfriend right now. Flirting and friendly conversations don't count for squat.
An exclusive boyfriend-girlfriend relationship only exists when one person asks and the other says yes, no exceptions. If both people haven't agreed to an 'official' exclusive relationship, there ain't no exclusive relationship. Neither you nor either of these guys have entered into a relationship yet.
If you get into an exclusive relationship with one person, it's usually understood that both of you will not date (or get romantically involved with) anyone else. But if you're just seeing someone casually, even if you're just casually f**king someone, you don't answer to anyone but yourself. And if you enter into an open relationship (meaning seeing, dating and f**king other people is allowed), you can have as many lovers as you want.
Most people won't agree to an open relationship, but some will. And since neither of these guys are your boyfriend (at least not yet), you don't have to worry about that stuff.