My sister has a kid with down syndrome and I really don't like him.

I never wanted to admit it to myself or anyone else, but I'm not used to being around people with mental handicap. I get really irritated when I'm around him and today I just broke down. I love my sister and the whole situation upsets me so much it makes me cry. I love her and I want to be there for her and him, but I can't. I hate myself.<br><br>If you can, advice please.