I once had a twin sister.  She never actually wanted to be my twin.  We officially broke up a year ago this month.  My sister always treated me badly, but I never wanted to see it.  In fact, I never was able to see the "real" her.  It turns out that she has Narcissistic Personality Disorder.  Looking back, that explains her lack of feeling, her complete and utter selfishness.  I never wanted to see it. 
She abandoned me many times.  I have learned not to trust her at all, with ANYTHING.  And I just deal with it.  But last year, she left her 4-year-old daughter to be with a guy.  She moved 800 miles away.  She didn't even ask to take her daughter.  She sees her maybe once every two months, for a weekend.  She doesn't see what's wrong with this.  I'm not surprised.  But I'm angry and disappointed.
My soon to be ex-brother-in-law is doing a great job as a single father.  I don't say he's a hero though, like a lot of people do.  After all, people end up being single mothers all the time. But, he is doing well, and my niece just ADORES her daddy.
I try to see my niece as much as possible.  My sister bitches and moans about it, but the court gave physical and legal custody to my brother-in-law, and he's fine with it.  I tell my sister to fuck off, and if she's so upset about it, she should move back so that her daughter has a mother in her life.  She won't, of course.  She has a new man, and she's living it up in a new city, drinking every night, going out all weekend, etc.  She says she deserves this "me time."  I told her that she doesn't deserve shit, and that once you have a kid, there is no such thing as "me time" anymore.

It's not like this daughter of hers was an accident.  It was completely planned.  After she lured my brother in law in, and they got married (after 8 months), she got pregnant right away.  After her daughter was born, she couldn't handle it.  I should have seen things coming then.  My sister went back to work almost immediately, and she paid me to watch her daughter every day.  After a year of this, I told her she needed to step up.  So, she sent her daughter to daycare.  Even on days when she wasn't working.  Whatever.
She wasn't harmful, just neglectful.  On days where I'd watch my niece, I'd get to my sister's house, and she'd be on the computer (talking to guys... She always has several in orbit.)  Meanwhile, my niece would be in a completely soaked diaper, crying and not fed.  It's like my sister hardly noticed. But, she LOVED showing my niece off to anyone and everyone she could.  God, I can barely stand her.  She's so phony.

More to come later....