Your son needs the best you have. Might include tough love for mom.
Establish pickup time. Establish civil arrangements you both expect if she fails. There are Control Issues with the MLCer. When you want to control your life or your son's, you're saying you want to cotrol her - and that means war.
Consistent efforts can establish a cut off time for changing pre-established pickup arrangements. It isn't on you to fold the tent and surrender your rights or your son's best interests.
Keep detail notes of what is working and what isn't. You may need to show you repeatedly try without reciprocation. You may have to defend allegations that you're a monster. She's evolving and may change without warning. You may be challenged on custody or accused of abuse. Not because she wants to be best mom, but because she suddenly needs to destroy all challeners.
Waiting for her at the home is like waiting on a door to door salesman. Consider a regular schedule of entertaining your son with activity at a park, McDonald, or any fun venue. It would be good for both of you to get out. It would provide a regular limited opportunity for her pickup in a public place. PlanB for you and your son could be lunch or movie, etc if she no-shows. Don't make excuses for mom. You both have grown up problems that make life hard, and might sometimes keep mom from being able to show up at the last minute. Such is life. Enter PlanB for everyone.
Amy gave great insight as always. There've been many writings here and in books about the human brain, behavior, and dependencies. By now you should have seen reference to 180s. That is the MLCer becoming the total opposite of their old self. That is you changing anything about your old self. There are good and bad 180s. Depressed people self medicate. MLCers at their core, are or become depressed. They might drink like no tomorrow. They might experiment with drugs. They might abuse prescriptions. They might seek new friends that don't judge thier changes. They might seek intimacy with someone new that 'understands' them; their new self.
New relations cause the brain to release natural chemical agents. The affect is welcome to the MLCer. It may stimulate highs they haven't had for some time; since depression. It may satisfy the new desire to please Self. The emergence of a new Super Ego is natural in MLC. They pleased the world and the world failed them. They must now please themself. It is addicting on chemical and emotional levels. It's their new monkey; a pet they enjoy at first. It'll eventually disappoint or fail them just as the world did before MLC. Once the monkey starts consuming all she has, destroying everything, and tossing cr@p at her - it'll be time for a new monkey. MLC starts out as a party. It begins to suck the life out of the MLCer; the only one that can stop it. The MLCer can't and won't listen while denying all prior logic. Everyone is wrong and no one understands, except the new monkey.
Some try to help and become the damaged bystander. New friends come and go. Some MLCers never make the decision to leave the party or develop the will. She could wake up a better person, or let the monkey destroy everything. Everyone else is blamed for her pain. Those who remain the closest are convenient to blame the most.
You're trying to understand without becoming stuck. Thank you. Many fight it, creating thread after thread about their painful existence in a desperate search of a cure for the lost loved one. People come to a place of understanding in their own time. We know where the new members are coming from, and we know their grief. We hope to see you and your son discover your absolute best in the days to come.