The day my relationship ended I wiped every trace of my ex out of my life. The sight of his name on anything belonging to me would make me feel disgusted,angry and stupid. It's just a reminder that I was in love with someone who I can't think of without saying ew. Him keeping her name shows that he was either never emotionally attached to her like I was with my ex or he still has feelings for her.
Her being unattractive in your eyes bugs you because external beauty is easy to compete against but inner beauty,depth, intelligence, humour etc. those things are harder to beat. You can't see what he sees in her which makes you question what he sees in you since beauty clearly isn’t his main/only criteria. You lead with your looks, she doesnt have those looks so she must have lead with something else,whatever that thing is,that's what makes you not jealous but rather insecure.
Insecurity isn't a weakness,it's a survival instinct. We need to feel secure in order to be vulnerable. If you are vulnerable without security your life is in danger. Knowing where we stand with people gives us security. Ask your boyfriend what he saw in his ex and stop making fun of her looks,it's childish, beneath you and it only makes your character look unattractive. And character is what you're up against. She maybe ugly to you but he clearly found something about her attractive.
