people who abuse friendships!!!!

ok, so i really that it's not always going to be rosy with your friends. a lot of things have been going on between some people that i'm very close to that has been upsetting me. one is it that people abuse the friendships that i have??? let me state a situation that happened to me and my sister; we feel very disrespected by this person; i'm not going to mention names so i'll just use initials.
M and her boyfriend breakup, she leaves the house they have shared for the last 2 yrs and starts calling some people to see if she can stay the night there. it's 2a.m so peeps are knocked out. she calls me, asks to spend the night, i say ok. she spends the night and leaves the next day. didn't hear from her until she wanted her charger. wanted me to leave it outside of my apt, so i did. doesn't call me but a few weeks later shows up at my apt when she finds out that her bestfriend was at my place. walks in and leaves without acknowledging me or my sis, matter of fact, asks another one of our friends to bring her purse down to the car since she had already walked out. haven't heard from her in a couple of weeks. M and her bestfriend have a falling out. bestfriend brings up the way M treats all her friends including the one's that she had stayed the night at. M states that the reason she has not called me or my sis is because we "are not friends like that". ok, does anyone see a problem??? if we "are not friends like that" why call and ask me if u can stay the night?? the many times she needed to study before class, M would call me and ask to study at my apt. so we "are not friends like that" after all the times that i opened my doors and accepted her into my house???? besides the point, M tells bestfriend that she would apologize to me and my sis the next time she sees us. we run into each other the next day, my sis and I smile and wave at her and try to speak to her. she treats us like we are her classmates, people she only talks to when she needs something. i'm not mad because she didn't call me to say thankyou, its her comment about how we "are not friends like that, i don't talk to them like that" that threw me over the wall. if u don't talk to me like that, why the hell did she call me to stay the night at my crib????????
why again do we abuse the friendships that we make in our lifetime??