THIS GIRL IS TRYING TO STEAL MY MAN!!! What can I do?

Well what happened was I found this girls number on my fiance's phone, what I didn't know was they are only friends. Anyway I got the number and texted it saying who r u and how do u know my fiance? She text back saying, how can he be ur fiance when he's married to me and we have a kid together and I live in bristol. Me and my fiance live in Manchester and the girl even claimed that he went down once a month to see her and spent 2 days at Hers before coming back up to Manchester (well that's a lie because he never spends more than five hours away from our flat) he never has and I've been with him for a year and 2 months and she said they got married in Bristol a year ago (funny he never left the flat in Manchester then) anyway I told my fiance everything she said and he laughed and said she was winding me up and if he is married where is his ring, and why is not with the kid if he had one? Then she started texting him telling him I was a cripple cos I have a disability and loads of bad stuff about me. I have a feeling she text him everyday and I have a feeling she's trying to steal him. I told her to leave him alone but she text back saying, 'im going nowhere me love so u better get used to it' I have a feeling she is trying to split us up also cos I'm not being nasty to other people when I say this, but she has four kids, probably by four different fathers, now she tryig to steal my man, she won't though, there is no way she can split us up me and my fiance r too strong and he won't leave me for anyone!