How to handle relationship with step children and child's father?

I'm a step dad to my partners 2 children. Their dad is heavily involved. Recently my girlfriend has been meeting up with her ex and kids for summer fairs and things. The kids told me, she didn't. She claims she hates her ex and he has another girlfriend. I work a lot so couldn't go with her. She also sent the kids school report to her ex but not me. I feed them, take them out, help with homework etc... I think it's great that the dad is involved but I'm starring to feel very left out. I'm jealous of her and her ex playing happy family's.

I'm guessing this is normal?

How to handle relationship with step children and child's father?
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