I'm so over this. At this point I'm not going to return my fwb's call
You sound upset with them. Why won't you return their call?
Yes, I saw him kissing my co-worker yesterday.
I understand you're upset, but usually when you have a friend with benefit, you understand they are allowed to do whatever they want. You shouldn't be getting jealous in this situation.
I will be mad and make him feel bad.
It sounds like you need to talk with him about your feelings, because I feel like you have more invested than he would expect from a FWB. Talk to him and see if he has any romantic feelings for you. If he doesn't feel the same I would suggest ending the FWB situation and moving on.