i'm worthless

So things have been really really good lately. I havn't seemed to have many cares at all. like really. even yesterday when a ton of shit happend with my mom, it only upset me for a little bit, and then I was fine, but I still find myself feeling sad in the back of my mind.
I now know why I have this feeling of sadness. and I really don't like this reason, but it is because of one person I am so sad. and I know that that will never, ever change, it's impossible for her. asking her to change would be like asking her to cange for me. and that isn't right. at all
it's not a bg really. I mean, I guess I don't mind it. i'm used to it.
I have always been the one that goes out of my way to make her happy, to make everyone happy. to never spend money onmyself. or ever ask for anything from her. all my money, from graduation, birthdays, christmas, everything, it went to them. and I still feel terrible because my graduation took over both of theres. they both finished school while I finished a bigger level of school, and so they wern't in the big picture, they were just in the background. and I always feel terrible about that.
Now, we had a very tragic thing happen to us, and I feel like its my fault. it's because of me that we are going through all this, and if I wern't here, this never would have happend. maybe it would have happend but it wouldn't have been bad.
I am not important at all. I can't change there lives, as hard as I try, and I now know, that by trying my hardest to do every fucking thing possible, I am getting in the way and making them unhappy.
so I guess I should just not help them? not do things for them?
there's the real reason why i'm sad, because of myself. I am upset with myself because no matter how hard I try, I will never be good enough, ever...
and it upsets me. a lot. and I really don't know what to do....
i'll just continue to try and make them happy. and not upset them. i'll give them everything that I ever wanted, but no one did it for me. so Iwill give it to them.....