Is this a normal behavior of a true loving girlfriend ?

My gf has some sort of a behavior problem with herself. She tells me that there is a fine line between she,her friends & me. I am ok with that. But what makes me feel sad is when I see her with her friends she always has something to talk about & she is so happy with them. She is happy with me too but sometimes we don't have anything to talk about. I wanna talk about those stuff which interests her the most. But she cant open up to me as according to her I've been her bf for the past 2 years whereas she knows her friends for almost 12-13 years, thats why she can talk about anything with them. Another problem is that, she says that treats me as her senior with respect as I am 1 year older than her but I don't want this age factor to come into play in our relationship. I even went as a volunteer to our school farewell party on my birthday. But when she heard the news she said that its a really stupid way to spend someone's birthday. BUT I just did it for her. I want to spend time with her on my birthday. That'll be the most special gift for me. I went to the farewell & we just talked for 5-10 mins & she said that her mom might come anytime & went away. I felt a bit sad though I was happy that I could be with her for a few mins. She has mock tests the next for days for preparation of her boards in February. We last chatted on Saturday, she told me how glad & happy she is with me but after that she says she can chat next 'maybe' on Wednesday night. What ? Is she a bookworm ? She is gonna study 4 whole days for MOCK tests ? She cant spare 10-15 mins to send an sms or call me or email or anything at all ? Now today only, she put a status on facebook saying 'Such a feelin's coming over me, There is wonder in most everything I see!', then when I liked it, she sms'd me & we had nice conversation for about 1 & a half hours in sms's. I'm really confused about my gfs behavior. Is this a problem at all or what ? Does she want to be with me ? We've had a break up before but some how we are together again. Is she cheating on me ?(That status said something to be suspicious about) Did she come back feeling sorry for me ? Please anyone help......