Roommate Problems?

I just moved in with a good friend of mine. Everything is going great except 1 thing (and she KNEW this before we moved in together). I am only at our place Mon-thurs. Thurs after I get done with cl and get off work I head to a town about an hr. away and spend the weekend with my boyfriend (I've been doing this every weekend the past year). She told me that's totally cool with her that it would probably be better so we don't grow tired of eachother. Well, like the first week we lived together and I am at my boyfriends, she asks me "you're going to be staying here on the weekends some now right?" To witch I was like "I am going to continue the same routine I have been for the past year. We talked about this. Remember?" and she said "I know. It's just that I thought since you have a roomie you actually like you would stay more. It's like I live alone". This pisses me off because I told her this. Also, why should it be a big deal to her?