This is very difficult.
A good house dog can be a wonderful, even life-saving family member, but a troubled dog may be beyond our capacities.
We had a wonderful greyhound for many years, and after she died we adopted another greyhound. Unfortunately the new greyhound, who was wonderfully happy at the adoption kennel, became very anxious in our home, needing 24 hour care. After two months we returned her to the adoption agency. As soon as we were in the kennel building (with lots of dog barking) she returned to her happy self. The agency reposted her, only for adoption to a multi-dog household. This is a common problem with greyhounds. They have lived in kennels all their lives, and some cannot live without other dogs. She was a beautiful creature, and remembering her anxiety that I couldn't relieve makes me sad.

We connected with a closer agency and eventually adopted Hazel, a pointer hound who has been one of the best companions of my life. I've built a cremains box so that eventually Hazel and I will be buried together.

My wife developed a very painful disorder and was giving up on living. We borrowed a Havanese for a test month, and the effect on my wife was so good that we knew we'd adopt a Havanese for her. She and Hava are now constant companions, and Hava has been an important part of her recovery. Havanese don't like being alone, but Hava just sleeps when we go out. Having another dog nearby probably helps.

The adoptions were a little more expensive than shelter adoptions, but they included the promise that if we returned the dogs they would be re-homed until they found a good fit. The people in these organizations were very supportive, knowing that sometimes an adoption just doesn't work out and that you and the dog need to start over.
I tell you so much to assure you that it can be good when you find the dog that's right for you.
Study breeds and dog behavior to get a clear idea of the kind of dog energy that is best for you.
If you search you can probably find an agency that will re-home the terrier.
The agency we worked with started their animals with temporary foster people who could assess the dogs and give a description of the dogs' behavior and needs.
I hope you can find a way forward that is good for all of you.