why does she do this?!!?

after 3 days of not talking to my girlfriend i got on facebook and saw she was on so i messaged her and we talked for a good half hour before i got off the computer and we were perfectly fine, we were being our normal goofy selves. well today i woke up, texted her goodmorning and havent heard from her all day yet again. i just dont understand why she does that. she has a lot of family issues going on right now but she is talking to/hanging out with her friends all the time, it just seems like she is completely ignoring me and only me. normally i would assume that she wants to break up but just last night she was talking to me about marriage more and how she has been having dreams of our wedding and a family and was asking me what was wrong when i was in a bad mood. it just perplexes me that someone who i supposedly "mean the world to" wouldnt talk to me. when we first started dating she warned me that we wouldnt talk everyday, but going three days without talking to the man you supposedly love with all your heart and want to marry? just makes me worry that she doesnt mean any of the things she says to me. am i being selfish by wanting her to talk to me as much as possible? or do i have a legitimate reason to think like this? we have been dating for nearly a year and we would go a day or two without talking, go a week talking as much as possible, then go a week without talking then go 2 weeks talking off and on and so on and so on. i dont know if she just doesnt want to take her frustration from her life out on me so she isnt talking to me or if shes wanting to break up or what ever else may be going on. she is the only girl ive ever dated that is like this, so im not used to being in this situation. any advice is helpful. thanks.