Aw bless you. A sad experience for first time owners and poor Stan too. He obviously needs more help than you are able to give him. At least you've reacted quickly in realising he's too much for you. Hope things are sorted quickly for both you and Stan. Good luck.
I hope the new owners are knowledgeable enough to help him - please point them in the direction of the forum as they may well need some help and support and the last thing this chap needs is another failed homing
This dog will have more homes than I've had hot dinners! Sounds like he has been passed a long to the next unsuspecting people willing to have a go. SH gal's advice of going to Doodle Yrust should have been taken up, they would have assessed the dog and ensured he would only be going to his next and final home. Poor dog, everything is crossed for him.
I also question how someone can go for 8-9 months and not realize what a muck they are making. The first few weeks when Lexi and Beemer played I swear they sounded like they were killing each other. So I looked up signs of aggression. Asked people who had lots of dogs. Asked friends who were dog trainers and looked up comments on this site. Frankly until someone explained that they were just play fighting, I was almost ready to rehome Lexi (as she was the more mellow one) and focus just on Beemer - because making sure he was a good dog was my responsibility. And I cried a lot that week thinking that was going to have to be my option. But I didn't want to wait much longer because I knew there would be a time when it would get much harder. Thankfully with guidance and help and reassurances from many people here, the three of us made it thru. But I don't think people realize how much time puppies require - at least these guys. Maybe other breeds are easier as puppies. Just sad for this little guy.