Is she disloyal or Am I too rigid? Me?

My gf with whom I am in a long distance relationship for about 1.5 yrs ...but haven't yet met even for once till now ... tells me she is attracted to her teacher (she is doing masters). She herself tells me that she thinks of that teacher , waits to talk to her and meet her , checks her online or offline status . I was pretty hurt after listening to this but she tells that she has no physical interest in her...just that her vibe matches with the teacher. Both of them often goes to the clg canteen to have coffe and gossip . But isn't this obsession? Is it okay for a commited person to have such attractions? If I tell something , she tells that since she is loyal to me she is telling me everything...but she doesn't want to change her behaviour and constantly defends herself. Please tell me if I am being too rigid with the concept of loyalty or is she being disloyal to me?