if this has been going on for 18 months, immobilizing and anti-inflammatories will only help temporarily, it WILL come back.
I think your physio had the right idea to start strengthening the tendon/muscles because it is a long term solution, it is just that it was obviously too much too soon.
You need to be able to exercise target muscles (VMO/GLut med/patellar tendon) without irritating the tendon (sounds like patellar tendonitis to me too). Getting a jumper's knee brace will help you do that. I might also try transverse frictions once the inflammation calms down as well.
If you find that it doesn't get better with physio, strengthening and bracing, I would suggest shockwave therapy (Extracorporal shockwave therapy) We use it a lot at our clinic for chronic tendon issues, it has a very high success rate.
Cheers,