Well me and this girl have been best friends now for around 4years and we tell each other everything. Recently though she has started to annoy me by interferin in my private business - by telling me to stop texting this boy who I get on really well with because she says he's going to use me and she's been telling me things to put me off him too. I know she used to fancy him and I think she still does (even though she claims to hate him). So could this be genuine concern or is she just trying to sabotage things out of jealousy? Xx

Well I think its 50/50 you never no,friends can tell you things because they think they are doing the right thing,but then again they could be telling you a lot of nonsense because they are jealous.
Just say to your friend that you no that she liked him but she doesn't anymore and you like him now and if he is all what she says,you'll find out yourself.
Your not being nasty to her your just saying you have to see for yourself

Basically its anice way of telling her to but out without saying but out.

Her motives take a back seat to her actions, so let her know to stay out of your business.