How can i stop being jelous/possesive?

i have this friend of mine (ashley) and we are really close... she says she treats me like her a brother.. but i got this other friend (michael) and well... evry gurl im close with ends up to him.. like my "ex" hu is know his gf... and ashley told me that she will try start talking to michael.. and i cant help to feel the fact that ashley might slip away from me.. nd i dont wanna think that way.. i need help :(.. how can i stop being jelous/possesive..