A year ago my younger sister (ys)(26) &amp; I (36f) talked about getting a house w/her boyfriend (23) &amp; my son (13). Since her &amp; her bf were only working parttime, we put it on the back burner. They lived w/my parents. 

In Aug, our niece(18) also moved in w/our parents.

A month ago, I found out ys &amp; her bf bought a house &amp; niece is moving in w/them. Mom &amp; ys were sheepish &amp; tell me "We were waiting to tell you. We just told Carol (niece's mom) today."

Most of my family doesn't have much contact with Carol. Lot of back story.

Telling Carol 1st hurt.Ys told me they kept it a secret from everyone, then says "Ann from work offered us kitchen stuff." 

Ys calls on move in day upset. Nothing is going right. I stop by to help a bit. When I leave, Carol still has not shown up w/the couch. Dad says we will go out to dinner shortly after 7.

7:45 I text ys &amp; ask if we're still going to dinner. Yes. A minute later she texts back "Dad said no cuz the weather's getting bad"

Monday, doing laundry at my parents. Dad says he owes me dinner. I say not to worry, we didn't go cuz of the weather. He says, "It had nothing to with Carol. We just got so busy &amp; we were going to come home so ys could take a shower but we didn't. We went straight out to eat &amp; I forgot to call you." Huh?

Ys &amp; niece come over to get more stuff. Ys says they're on a schedule because she has to pick bf up from driver's ed (My dad paid $300 for him. His mom didn't allow him to get his license.) She asks me to move my car out of the driveway, which doesn't make sense but I do it. I'm pissy. I come back in &amp; she keeps talking. I'm aggravated &amp; yell "I moved my car. You'd better get going since you have a fucking schedule to keep."

I gather up my stuff and started ranting:

You're all fucking lying pieces of shit. The fact that you hid buying the house from me meant you knew you were doing something that would hurt me. That was my plan with you &amp; you went behind my back. This is bullshit. Then you fucking lie to me about dinner last night. What was the fucking point of that? &amp; no one gives a shit about what's going on with me &amp; my stuff. Nobody asked how my doctor's appointment went at (city an hour away). Nobody gives a flying fuck. &amp; when ys was having her mental breakdown &amp; you were out west who took her to the doctor? Who helped her unpack your whole house while you were out west? (Parents moved, left all their stuff in a mess, 2 days later go out west). She promised to help me clean &amp; organize my house for a couple of hours 1 weekend but any time I asked her she never had time for me. She forgets who was there for her when she needed help. I'm sorry that I'm such a 2nd class citizen to you. Oh, &amp; just so I don't get accused of anything (I then take off the spare key I have &amp; throw it on the counter)

During my rant ys ran upstairs. Mom chased after her. Dad sat in a chair looking at me like I'm an idiot.

So, am I the asshole?