First of all, I'm hope you are coping ok.
The surgery you had is not such a common surgical procedure and sometimes it fails. For the sounds of it, what they did was to cut your patellar tendon and reattach it to the bone, to make it shorter and realign your patella. The problem is, you see, that sometimes the reattachment site is not very strong and is detached from the union site. Unfortunately, because is a rare procedure there are no statistics about it. I checked with one of my friends (an Orthop surgeon) and he says that you need to get some x-rays done and maybe another surgery.
I'm sorry you are feeling down. Hope it helps.