Priority Number One

My Mom is out of town.  This of course means that my Grandma got so sick we had to put her in the hospital. 
I got a call from my Mom asking that my sister and I go to see her.  My sister decided that she didn't want to go because she wanted to go see her boyfriend.  She took the car.  On the phone, I snapped at my Mom, yelling "I already told you!  I can't go!"  I was about to yell more things when she hung up on me.  Then I was even more angry because my Mom hung up on me. 
It made me so angry to see my sister, in her usual scrubs, watching tv.  That's all she does when she's at home, other than the occasional homework.  She's taking what she calls an easy summer class, and she can't be bothered to see her Grandma in the hospital because she needs to see her boyfriend.  Not work on her homework.  Her boyfriend.  Priority number one. 
There are a lot of reasons this upsets me.  First off, my sister has not been to see my Grandma the entire five days or so she's been in the hospital, but I've been in several times.  Secondly, she decided the boyfriend was more important.  And lastly, she'll probably get away with it.
Sometimes I suspect my sister is given more leeway because of this boyfriend.  When we're on trips, she always gets to talk on the phone for him to hours.  I don't.  I don't have a long term boyfriend, and I don't usually tell my Mom about my trysts because I don't consider them her business (also, because they immediately become the gossip of everyone who comes into our house for the next six months).  My sister is allowed to bring him to family events, is allowed to hang out with him instead of doing stuff like helping with my Grandma.  My family holds this hetero-centric, monogamy-centric ideal so high that it allows my sister to take advantage of it.  It gets me angry sometimes.  Like now, when it's my Grandma's birthday, and I can't see her because my sister has the car to visit her boyfriend and I'm stranded alone at home.
After my sister left, I went outside for a little, trying to work off my anger.  It didn't really work.  All I could think of is how selfish she is and how nobody seems to notice and how she takes advantage of this.
When she got home, my Mom made another upset call, this time to my Dad (who had finally come home) about moving my Grandma out of the hospital.  At that point, it looked like my Grandma was going to be released the next day.  She was apparently going to need some help getting home and then someone was going to have to stay with her for the night.  I volunteered to help with both, though a second person would be needed to help with the moving her back to her apartment.  When my Dad asked her about it, she said, sitting there, in front of the tv, again, that she was going to the park the next day and wouldn't help. 
"Well, I can't do it," my Dad said.  "I'm working." 
My sister just repeated that she wouldn't do it.
Watching her, again, in terrible clothes, watching tv after coming home from seeing her boyfriend for five hours, too lazy to take harder classes, too lazy to do something with her life other than an occupation that she doesn't really care for and that is easier than others, too lazy to contribute all week when she's been asked to do so, made my blood boil.  I wanted to punch her. 
"Well, than we'll take care of it," I said, meaning my Father and I.  Because apparently she wouldn't.  I started walking out of the room.  This conversation wasn't going anywhere. 
My sister said something nasty in reply, but I was so angry, I can't remember what it was.