I know a farm that recently lost their teaser stallion. He was a stallion that they had used to cover mares, but then the honestly had a much better stallion (hall of fame better) that they wanted to use/had bred. This current stallion is standing at stud out of state, so all mares on the farm are either AI or shipped a few days before ovulation. The teaser stallion was easy to handle, was 18 at time and was able to indicate a mare was in heat and receptive which allowed them to get the vet in to do an ultrasound to measure follicule size.
Its not a bad life, its the life of a stallion. He lived by himself, was stabled with the mares at night and never threw a fit. He was easy to handle, had a job on the farm and was really well loved. There were worse places for him to end up. In all honesty he had retired from being a "professional stallion" and his owners did not want him to end up somewhere bad. They figured after nearly 20 years being a stallion and being well mannered it was okay to use him as a teaser. That said, he was not at your average down the street farm. Its a serious farm with seriously well bred horses.
Being a teaser stallion is not a job for every stud, its a job for an exceptionally mannered and minded stud. A good teaser stallion indicates and shows interest but is not un-managable. Most stallions and horses in general don't sit around feeling sad they did not cover a mare. 1/2 an hour after the mare leaves the area they are not writing love songs and crying into cherry garcia. The teaser stud also needs to be on a farm where there are significant numbers of horses. The barn in mind had 18+ mares in foal at any one time. The teaser is not that different or sadder than a horse that is trained on AI. AI stallions are trained to a dummy and don't even get to mount a real mare. I know of AI stallions that drop at the sight of the vet who collects them not the mares. They are trained using a mare in heat standing right in front of the dummy.