Advice needed

Edit: sorry bio dad is NOT on birth cert. It’s mentally tormenting me that I will never have the same name as my child and while some of my reasons may seem petty I can’t help how I’m feeling.

;

Bit of a head scratcher and I need advice

My ex partner isn’t the bio father of my 18 month old but for all intensive purposes he is her dad. We were together while I was pregnant with plans to marry.

I was so convinced that he was it that I gave my little one his last name when he was born to save changing it when we married and I changed and we’d be a family. Wishful and dumb thinking.

We broke up for good 4 months ago and I want to change his last name to mine but I know it will cause an uproar.

We share custody because blood or not he has been his dad and involved from day one and while towards the end not a good partner has always been a good father.

He’s not on his birth certificate because I know the bio dad and just left him on it.

I know my family will berate me for cutting the name tie and ex will be incredibly hurt as he intends to stay his dad but I need to feel justified that my son should have my last name,