How to help stepdad feel included?

My partner of 3 years is an amazing step dad to my 2 daughters 14 and 10. Their biological dad is still heavily involved and they spend quite abit of time with him.

There was an event that came up last week for my 10 year old at our local university where she was presented with an award. Me and their dad went together and my partner stayed home. He said that watching me get all dressed up to go out with my ex for the evening was strange and made him feel uncomfortable.

He knows I hate my ex but we have to this for the girls surely. He said we should have gone together and my ex and his partner should have gone too.

My ex thinks it should always be just me and him and my partner is feeling excluded. Anyone else experienced similar?

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I'd say European men are more open and more adventurous in bed.
How to help stepdad feel included?
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