dunno what to do anymore

I've been with my boyfriend for 3 year's now and everything seems great but thing I'd ive got this friend she hardly talk to me but she mostly chats to my boyfriend insted I've seen messages on his phone she calling him gorgeous nf other well seems like flirty message I try tlk to him about it but I shy away cause I don't want to start an argument but they worry me and stuck in my head when he says he going out I alltomacticlly think he going to her and I get up set with him and causes problem with, our relationship