My girlfriend puts me last?

I feel like this is a stupid question to ask since we are both in our 30's and are way too old for these stupid games but I'll ask anyway. We have been together for about a year and a half and during this time our only problems have been because of her inability to communicate, she always puts me last before her family, and does not ever go out of her way to do anything for me. I understand the family part and it is part of what I really admire about her but it has it's downsides. Due to our current situation we do not get to see a lot of each other. We basically only get to spend quality time every other weekend. I rarely see her during the week. The time that we spend together on the weekend is often cut short or canceled due to a family member needing her to babysit or nieces and nephews needing her help with something. We actually haven't argued about this in about 8 months because I have just been letting it slide. She can't ever make plans. She can't ever show up on time and if anyone in her family needs anything she suddenly cancels our plans and takes off. I recently had a birthday and since she doesn't have much money, all I told her I wanted was for us to go out and for her to spend the night. She agreed and said she could do that 2 weeks before my birthday. On the day of my birthday, FOUR hours before we were supposed to go out she called and said she will have to go home early and can't spend the night because her nephew needs something from her at 9 in the morning. I think it is great that she wants to be there for him but she had the opportunity to be there for both of us...it was just to difficult for her to be there for me. I live about 5 minutes from her house. She would have had to get up 5 minutes earlier in order to be there for her nephew but this was "too much of a pain in the ass" for her. I was very upset since she can never follow through with anything, and especially since it was by birthday. Planned 2 weeks ago and changed 4 hours before we were to go out. I do everything for her and constantly go out of my way to make her happy. I believe relationships should be give and take and each should be considerate of the others feelings. I am and obviously she is not doing a very good job at it. I have tried to talk to her about this but her only response is "my family will always come first" and "its a pain in the ass to get up and drive home". We had been talking about getting a house and getting married. Shouldn't I be just a little more important to her? Especially when I never ask her for anything but a little bit of her time every other weekend. Now she is playing the silent game because I got upset with her about my birthday. This is childish and our relationship will never go anywhere unless she learns to take my feelings into consideration and talk things through. I'm pretty sure I know the answer...get rid of her...but it's tough. She is a really great person...just likes to leave me hanging. Thoughts?
My girlfriend puts me last?
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