Cant stop worrying its ruining me :( advice?

Hey everyone,

The past couple of days i cant stop thinking and worrying that my boyfriend is going to leave me.

I dont know why or where it has come from i really love him and i think he really loves me but i just cant stop thinking about it lately its really worrying me it puts me in tears everytime i think about it.

Iv told him and he says hes not going to leave me but i just dont know

Im getting sleepless nights its ruining my work life and my day to day things

It seems to be on my mind more and more each day! Please can i have some help/ advice? :(