Is it normal to somewhat lose your best friend as you get older?

I'm sixteen; so i'm not real old but when my bestfriend and I were growing up; first grade to the middle of ninth grade we were real close. Until we both got boyfriends, but my relationship lasted and hers didn't. I've been with my boyfriend for a year and seven months. Lately i've been wondering if its normal to lose a close friendship because of having a relationship. I love her and I love him as well. But I find myself seeing him alot more than I see her so far this summer, i'm with him probably three times a week and i'm only with her once or she stays all weekend with me at my cabin or salt lake or my aunt. I will always be there for her, but I know she hates my relationship and she doesn't like my boyfriend either. I can't even have them into the same room without him joking with her and her having a fit. I don't blame her not to like him, and I honestly don't care. But I feel like she's only there for me when my boyfriend and I fight or one time we tried to take a break because we were fighting pretty badly that week and I felt she was there for me that week than she was there for me since before I was dating him. I just find myself wanting to just be with him and my family, and I feel like he's my bestfriend because he's always there for me now. Is this normal? Or should I try to be with her more often? I know i'm still young to be devoted to a boy but I am and I don't know if it's good or bad because of my loss of interest in my bestfriend and friends.