bf “talking” to another girl

Isabel

so recently my bf has been talking to his girl coworker a lot. on every social media platform and even texting now. at first he would tell me like oh we just send each other funny stuff but what could you possibly be texting about. and he talks to her on a daily all the time. I always see her name pop up in his phone. so I asked him about it and he got defensive and said “oh i’m not allowed to have friends” of course he is but the amount of attention he is giving this girl is crazy. then I was talking with his brother and telling him how I felt about this girl and he told me that my bf said that this girl wants his dick so bad and then his brother asked him if he would ever get with her and my bf actually said “ I don’t know” he contemplated being with her when he knows I don’t like her at all. so I asked my bf to be completely honest with me and I asked if he’s ever contemplated her in any way and of course he said “never” and he gets mad at me now for even mentioning it and he won’t tell me what he would text her about. so I just need some advice what do I do. I promised his brother I wouldn’t tell on him and tell my bf I know what he said bc I wasn’t supposed to know. but how do I move on knowing he contemplated being with another person. i’m miserable and my anxiety is soo bad. I feel sick to my stomach I can’t eat and I can’t stop shaking. someone help please