I need help!

So my boyfriend of 5 months has gotten a new job and he's had it for a few weeks now and he does so good at this job and it's a factory job, so he gets pretty good pay... well I just got news from him the other night that his crazy ex gf started working there. This is an ex that he had a lot of history with, and he told me he still had some feelings for her wayyy earlier in our relationship.. I still trip about it now, but he says that the way he felt about her can never compare to how much he loves me. But when I found out that she started working there I was filled with such rage! Like that's my man.. he left you, stop following him you loon! I just don't know what to do or how to express how I feel because asking him to leave his job would be horrible of me to do, and I don't want to be that girlfriend but I fear every day what she might say to him, I trust him but I have no trust for her snake ass. Someone PLEASE HELP ME!!!