My hands are so gross :(

Hi everyone, I'm so happy I've found this site - I'm sure you all understand! I have been picking my knuckles since I was about 18 I think - can't remember exactly but I'm now 29 and I'm so ashamed about it. My fiance is constantly telling me to stop because "look at your hands!!", which just makes me want to do it even more. He doesn't seem to understand I CAN'T!!! I don't know why I do it, I'd really like to know, but more than anything I just want to have nice hands. When I got engaged I was even embarassed to show my family my ring because I was scared they'd notice and say something. At the moment my knuckles are just like callouses - so gross. I also pick the skin on the area behind my knuckles, which are meant to be soft ... but not so much. I will also pick my lips. Sometimes I don't realise I do it, but sometimes I do and I feel like I need it - like it will make me feel better or something. When I get stressed my knuckles can get so bad the skin breaks, and because the area is so dry it really hurts. Sorry, I know it's gross, but I'd really like to know if anyone does anything like this, or knows how I can find out why I do it??