I have been talking to my best friends sister off and on for a couple mounths and...

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...its really complicated.? Alright I have know this girl my whole life, and I have always had a crush on her. But its has always been one of those things that you would think about but you never thought it would happen. Just a few mounths ago we ment up and she started talking to me and i really didnt expect it. I mean this is my best friends sister, we have always been real good friends but it just seemed weird. then we actually started talking and we went out on a few dates, and things were ok between us but i never knew what to say to her brother. I mean what am i going to say hey man me and your sister are getting close.But anyways since i really have not settled things with her brother we have been on and off for awhile because i guess she wants me to own up to her and i really dont know how.I just need some tips on what i should do with the situation.She told me last week we should just be friends for awhile unitl we mature.And ever since than i have ignored her text its been a week what should i say?