This has nothing to do with vengeance. He is doing what is totally predictable for him. The absolute minimum he feels he can get away with. And the bit about leaving because he had "permission" from the meeting leader? Total BS. Probation requires that he ATTEND the meeting, not that he get a piece of paper signed. The paper is only proof that he showed up. When I am the meeting leader, I won't sign papers until the end of the meeting, and if someone showed up fifteen minutes before the end, I'll refuse to sign it.
And if he were MY probationer, and I saw he fulfilled his "requirement" by attending three meetings in one day, I'd certainly know what I was dealing with. Someone who will screw up, probably sooner rather than later.
I hope you will start putting your energy into your own recovery and stop trying to manage or "help" with his. He is going to do what he is going to do (or rather, not do what he is not going to do) and you need to be in a position where you can take care of yourself when the sh*t hits the fan.