I was the same when it came to DH's family, I would let everything they did and say get to me and I spent so much time worrying over it and being upset by it.

IMO it's a constant battle, I have to remind myself that it doesn't matter. When I feel myself getting worked up over something I stop myself and say, it doesn't matter. I remind myself of all the wonderful things in my life and concentrate on those.

I think the only way people change is if you are constantly working at it, constantly stopping yourself when you're thinking one way and make yourself think a more positive way.

Thats what I've found has worked, took me a few years to realise it but it works for me now. I still get upset by things from time to time but have to snap myself out of it and think a different way.