I'm always overthinking

Me and my boyfriend have been dating for a year. I love him a lot at I trust him. Right now we're doing the long distance thing. It sucks because I really want to be with him. The problem is he has a good number of female friends. Even though I know he loves me and I trust him every time I hear about them I get anxious. I don't know why! He's never given me any reason not to trust him. I know me getting anxious stresses him out but I can't seem to control these feelings of mine. Please help.