I really want a cat but my parents wont let me!?

im sorry I have asked this before but no ones answers are working... I want a cat a lot! my little sister says im being stupid for wanting one... I don't care! I want a Companion who will love me and be there for me because i am very emotional.. My family has a dog but the dog only wants to be with my mom and it ignores me and crys at the door waiting for my mum.. I have offered to do everything from cleaning the box to vacuuming every week to minimize cat hair.... My moms answer is just No... she says I hope you get a cat when you move out...and I hate it when she says that.. I don't want a cat later (I have some serious serous about growing up and moving out that I have never talked to anyone about) I want a cat in the near future...I was thinking about going to college 15 miles away so I could live at home but now I don't know what to do. I don't just want a kitten and then like I will be all bored with it in a month. I am willing to adopt a shelter cat to give one a good home...Please Please Please help me.... My parents do this a lot... about a year ago i was interested in getting a hamster or some small critter...and they said the same thing... "NO RATS IN MY HOUSE!!!!" My mom comes up with a new excuse every time I bring it up... I don't want my house to smell...IT will shed all over...It will claw up my couches.... PLEASE PLEASE help me...