Is it possible to be gay for one person but you know you’re striaght

I’ve been in a relationship with my gf for over 3 years . I’m a girl ofc but recently she told me that . She can’t see herself with any other girl but me but she can see her self with other guys . Like she doesn’t know her sexuality . She can’t see herself doing all these other stuff with other girls . But just me she says she loves me and we’ve done stuff but she like isn’t attracted in that way with other girls but men . What does this mean ?