Will things be stable now, or could he experience a relapse, given the involvement of extraterrestrials having targeted him to get him to go over the edge?

Unfortunately, your fears are justified. He is not out of the woods because he is a targeted individual. So time will tell how long it might be before they go back at it, to start a new campaign to commandeer his mind, alter his thinking and judgment in a similar way. We will endeavor to keep him protected and with ongoing healing sessions being done to support him, this is possible to do, but unfortunately, is necessary as long as he is targeted in this way. If he avoids drug use, that will make it easier to keep him safe. We are endeavoring to help reinforce his newfound conclusion that getting high has cost him. He is correct, and will not be above slipping back into a nightmare if he gives in to temptation, thinking he can manage it and keep it under control.