Marital advice!

So I am married, been married for 2 years. My husband has a son from a previous relationship. I am truly, and honesty struggling to get over the fact that my husband is friends with his sons mother AND that they work together. I know I need to count my blessings and I do!!! But it seems like every week they do something that makes me uncomfortable and if I approach my husband about how it makes me feel I am the bad guy! 

For example... I know this isn't a big deal but last night was my step sons football  game. I couldn't make it due to work. But my husband and his ex made it. They sat together the whole time. My husband didn't even tell me until I asked later that night. That makes me feel weird!!!! 😞 They already work together and see each other every day, but now they have to sit next to each other? I wish it didn't make me emotional and I don't know what to do!