Halloween

So my son's father and I have 50/50 legal, but I have placement of my son. We have no set visitation through the court, just that we will decide reasonable parenting time as well as holidays. He typically has my son 30hrs a week, Tuesday, Friday and Saturdays so I can work. I have my son all overnights.

This is my son's first year trick or treating. I already bought his costume and I want to take him out that night. It's on a day his dad usually has him. I just have him a months notice that I will be taking the day off to spend with my son but he can have him another day that week so he doesn't lose time.

A little back story, his dad was very abusive towards me and I left him 4 months ago. He's had a new girlfriend for about 2-3 months. He's broken our custody agreement by letting her meet my son. (We are supposed to wait 3 months and I'm supposed to meet her before my son does, both of which he has broken). His dad is giving me push back on this, but I'm honestly crushed by the thought of this woman spending Halloween with my son and not me. I think it's completely inappropriate. This man has taken so much from me already, I don't think I can handle losing any more special moments with my son.

Do you think I'm within my rights here?