Jealous of this awful woman? Why?

There is this woman who i believe fancies my boyfriend, she is just an awful woman (cheated on her husband) and i really don't like or trust her, her husband is my boyfriend's boss so they see a lot of each other. I do trust my boyfriend and know that he loves me a lot, but every time i see this woman i feel irate, like she wrote on his fb wall for his birthday today "happy birthday (pet name for boyfriend) have a good 1 babe, love (her name)" and i am literally trembling with rage, i cannot stand her!!! I get so jealous even though to be honest she's not good looking and i'm pretty, not to sound lika a b*tch, but i only will call someone ugly if i see that they are bad on the inside as well as the outside. Anyways, what do i do??? I'm so upset!!