What to do when husband forgets his own son?

Now that we are separated, my husband has made a big deal out of having dinner with our son, a high school Senior, on Thursday nights--just the two of them for "boys night out". (Perhaps it goes without saying that Thursday was chosen because of its supreme convenience for my husband, although a Thursday school night is far from ideal for a kid struggling with his own Dyslexia/ADHD homework challenges.) Husband has now blown off two of these Thursdays in a row. I'm not at home (teaching night class) while son waits at home to hear from dad, too worked up to feed himself or focus on homework--just seething in limbo. Last Thursday's getting blown off was never acknowledged by husband. This Thursday, husband called son to ask him to do him a favor, completely oblivious, at 11 pm, that he had never shown up for their dinner. Son was terse, hung up. This morning, son finds apologetic text from Dad, sent at 1 a.m., which son reads aloud in a pitch-perfect impression of my husband's all-too-familiar self-pitying groveling voice he has used countless times when he is "caught" and trying to get out of something. Please internet community, what the ^&*% should I do? I can't tell this boy that up is down and poop is really ice cream. I can't negate his very real/justified anger with his father. What's the value in teaching a child not to trust his own feelings and instincts, or to train himself not to feel hurt, not to assert his right to be seen and heard? On the other hand, because this is my husband (the grand painful tornado of destruction in my own life), I cannot fall into the trap of projecting my own fury onto this situation. I cannot be the mom who badmouths dad in front of the son. And this is the only father he will ever have...so no matter how painful...this is not a relationship to encourage an 18 year old boy to reject when he tells his mother he is "done" with dad... And then there is the elephant in the room: This man cannot/will not change. Every/any bright shiny thing (students who worship him, strangers who find him fascinating) will always have more appeal than subjecting himself to the disapproval of his family, to entering into situations where my husband has to take responsibility for those he hurt and actively rebuild a relationship. I know this pain so well. It kills me to see my son experiencing it. Nothing will change unless my son, at his tender age, takes responsibility both for expressing his pain and rage to his dad, and for creating a solution, some way that they can rebuild the relationship. My husband is incapable of that. Should I encourage my son to take on that burden? Is it doubly unfair to do so, given that whatever the kid does, it will probably have no effect on his father...? Not sure if this even makes sense. Sincerely open to thoughts from anyone who has walked this path...