Why does this betrayal of friendship happen?

I have a friend for 7 years. We were close. Her uncle threw her out of the house and she had no other family. I gave her shelter and food, paid for her bills while she was depressed, and when she got better, I gave her a job at my office temporarily even during a rough time financially. I never charged her rent, food, bought her new clothes and paid her a good wage much to my fiance disagreement about hiring her. A year later, I was going through a rough time with my fiance. We had arguments often at home. I crashed physically and emotionally for 3 months and couldn't work. Then when I came back to work, she started to resent me. I was told that she wanted to have a share of a project my fiance got going at work. My fiance and I got married. She told my mother that I force him to marry me for the money (he is totally in debt). She didn't go to my wedding, moved out when I wasn't home and stole the files at my office. We had never argued. I am confused? What happened

it sounds like this so-called-friend got a real bad case of the big head and thought that she would just take over your business. she obviously didn't appreciate anything that you did for her. it's a sad thing, but sometimes when people change, it's not for the better. she probably got to thinking all this during the 3 months that you couldn't work. and when you came back to work, she didn't like it because she realized that the real boss was back and she couldn't compete.
I'm really sorry that you were taken advantage of by someone you thought was your friend. but remember, you did everything that you possibly could do to help her when she was down and out. that says a lot about the kind of person you are.
I really can't tell you all the reasons she did what she did, but I can give you a little advice. never let yourself be taken advantage of by her again, she is not your friend. and you and your wife go on with your lives and be happy running your business together.
Best Wishes, you really sound like a wonderful person.

i dont know i wasnt really paying attention

Damn it sounds like u were used. Sorry that happened to u, although u guys had been friends for 7 years, for her to treat u like this she really wasn't ur friend to begin with. Just take it as a life lesson learned, u r better off without her.