Women help me out is this normal?

I am dating this women for about a year. After two months she starts leaving in the middle of the night to go to what she says is a friends (girl) then we talk about it and it stopped for a while. Then it starts up again but she thinks it is ok because she is now telling me where she is going. I am not stopping her I just want to know if other women do this on a almost nightly thing. I don't like it I asked why would she not go to see her in the day time and she tells me it is because I don't like to go over her house. It should not stop her from going there just because I don't like to go over there should it. I like her friend I just can not sit there for 2 to 3 hours with out something to do there is no t.v. in the living room and I would frrl funny to go in there bed room to watch t.v. help please.