I suppose it must feel like they are taking sides with him rather than you?
Whereas they are doing their best to be fair to both. He will have asked them not to divulge his whereabouts to you so they haven't, and it would be the same if you asked them to keep something from him. I do understand it doesn't feel fair that the offending party gets treated the same as the "victim" here, but try to see it from their point of view trying to negotiate the tangle of separating parents.
I can also understand the indignation that you dealt with the emergency, all the hassle, all the worry & all the stress with no support or anyone to share it with, then he appears after the event to have the major part in the happy ending with only a minor effort.
But at the same time great news about DS!