I love my parents, but I don't know how to show it...

I'm at university and I moved out from home three years ago and now only goes and visit my parents during holidays. Everytime I go home, my dad would have gained more white hair and it makes me sad to think that someday they won't be there anymore. I love them, but I don't know how to show it. Nomatter how independent and strong I am while away, when I'm home, I'm a little kid all over again. I don't even wash my own cloths, and I still leave my room in a mess. I only goes to them when things are difficult in my life... I wish I could share the good times in my life too... I don't know, they just don't seem that interested. I used to fight with them alot when I was a teenager and said some really harsh words. It bothers me that I did that, when they've done nothing but trying their best to love me. They've sacrificed so much of themselves for me and I don't know what I can do for them. I don't know what I'd do the day when they're not there anymore...