I agree with B.
I think you and your ex are jumping the gun on a lot of things. You should not be introducing new dating partners to your child at this point. Children get attached, and then if the dating relationship doesn't work out, the person disappears and children get so confused. It's irresponsible. Secondly, your ex's girlfriend should NOT be driving your child around, whether she's 18 or 28 or 38. This is your ex's responsibility, and if he cannot take time off from work to see his son, then the son stays with you or with an agreed-upon family member. You must stop agreeing to all of this. You say "okay" but it's really not. Third, she does NOT get to post pictures on social media of this child. He's not her fun little fantasy baby. Fourth, 14 month olds do not understand Halloween or trick-or-treating. Getting them all dressed up to go ringing strangers' doorbells is all about what the parents want, not about what the child understands. This is going to be confusing and possibly upsetting for your son, and having him do it twice is parental overload. You are the mom and he is the dad, and you can do what you want on your own time, but just be prepared for tears and stubbornness rather than the fantasy great time you both anticipate - that really happens when they are 5 and up. And please make sure your ex goes over the candy treats to pull out anything that is a choking hazard.
I have no idea what this "12th for their anniversary" day off is about, but it sounds very juvenile and something he is doing to keep his girlfriend happy. It's a red flag for me that he has his "anniversary" off but doesn't always take his son when he can and should. That should set off alarm bells with you, that he's not focused on being a father and far more focused on his new and exciting young girlfriend. If
Do you have a custody arrangement? If you weren't married and divorced, maybe you have nothing written up by a lawyer or the court, and it's just a casual agreement with your ex. If there's something legal, stick to it. If it doesn't work, file for a modification. If there is nothing legal in place, I think you should at least have a written visitation agreement that deals with custody, medical decisions, educational decisions, religious upbringing, the introduction of other love interests to your child, and so on. Your ex can either commit to a schedule and stick to it even if it's inconvenient (that's called "parenting" for his information), or you can have full custody and he can contact you now and then when he is free and see IF IF IF i's convenient for you to adjust your plans so the child can go to his dad's. The drop-off and pick-up should be by the DAD only, not a third party, unless their are grandparents involved and you both agree to this. There's no way a new babysitter/girlfriend, with questionable driving ability and nerves, should be involved at all. If she wants to have fun with a child, she can get a job as a nanny. She's not to play house with your child.
Please take a parenting course with your ex, including toddler first aid but also including decision-making and co-parenting.
Otherwise, this current situation is going to be disastrous and your child will pay the price for it.