His ex

My bf, soon to be husband’s ex cheated on him. They were together for 5 years. I recently found that she is getting married to very rich and influential family. While my bf is struggling in his career. Idk why am i feeling bad, i feel like i am horrible person that this thing is bothering me so much. Like she hasn’t done anything to me, then why am i feeling this way?? Also, how do you get over retroactive jealousy?