HELP‼️ 😞😞😞

OK so the other day I added a guy on Facebook that I knew from high school and I only added him back because I had remembered he did photography and I thought he could do my boyfriends pictures for the low because my boyfriend has been needing head shots but its so expensive, so I thought oh maybe he could do my boyfriends pictures well my boyfriend got a girls number from a friend that was talking to her on FaceTime and I caught him in a lie and he even deleted the thread of their messages ( even tho i had a pic of the thread im my phone) I am honestly so hurt even though they were just texting it hurt me so bad because I do not text other guys or communicate with other guys and for him to do this just hurt me so bad and I don't know what to do now. What's even worse is the night before he texted her I had expressed my feelings to him and finally told him that I had loved him. I do so much for him that I'm feeling so hurt that why would he do this to me I cook for him I do his laundry like we live together and I just feel like why would he even feel interested in another girl. I've already told him how insecure I am because of me gaining weight during our relationship and we're about to talk but I'm just so scared and hurt because I trusted him.