Coparenting and new partners

Hi everyone,

I have a question on how to navigate this new phase in life.

So my ex and I have an almost 4 year old. We've both dated other people and have agreed to let each other know when we were ready to introduce someone to our son. About a month ago, or so, I found out through my son that he had already been introduced to my ex's new gf. I knew this would happen, one day or another, but I never thought my ex wouldnt tell me. I always respect as my son's parent and as an individual.

When I asked him about it, he denied our son being introduced to someone. He said our son was lying. I brought it up twice and decided to just let it go. Last night he said "im ready to introduce Matteo to Sophie". I told him, I was already aware Matteo knew her because Matteo just naturally tells me everything. I never pry imformation out of my son, we just always talk and have a great relationship.

I did let my ex know it was very hurtful as a coparent to find out through our son, and not in the way we had mutually agreed.

This morning, Matteo comes home and tells me he spent the night at her house. Yes, I understand and know one day they will live together and Matteo will be there. But my thing is: his dad just denies everything and I honestly know nothing about this woman. I didnt feel comfortable that our son stayed at her house because I dont know her. Sometimes Matteo tells me he likes her sometimes he tells me he doesnt like her. I know its a confusing time for our son. And I want to approach this new life hump in a peaceful and respectful manner.

Has anyone been through something similar? Or what has your experience been? I'd like to meet her and make sure there are healthy and respectful bounderies set in place. But i am not sure how to go about it. Any any advice is appreciated. From both sides. As the step parent and as the parent.