I am so sorry to hear about this, because it is one of those things I can relate to. Recently went through something similar, and still am. First off, have you been to a doctor for the tendonitis? Can they do anything, or does it have to heal on its own? I do not get depressed but I do get frusterated and have a very high metabolism so I to use weight training and boxing as an outlet for that. About 2 months ago, I threw a softball from the left field fence to third base. Good news I got the runner out, bad news I felt my right shoulder pop, no pain just a popping sound and now it does that everytime i rotate it. Well I thought nothing of it, I am invincible right???? All the next week I hit the gym, on friday I did Biceps, light triceps and shoulders. To my horror, most of the strength in my right arm was gone, like I said there is no pain, but I can't lift even close to what I used to and my left arm is a lot stronger than my right now. I stopped going to the gym, not really sure why, maybe I didn't like to be reminded something is wrong. This is totally the wrong attitude to have and i thank you for your post because it have shown me something I lost in myself. Don't give up on what you love to do. you can still work your legs and torso, and cardio as you said. Hopefully the tendonitis will go away with some rest. If not look for other treatments, I so hope you find one, or and I will pray for you that it heals with time and rest. A lot of people won't understand your problem, but I want you to know I do and am here. Having a passion for anything and then losing it suddenly is painful and hard to cope with. Just keep looking for solutions and I am sure one will turn up. Being a weight lifter I am sure you are familiar with drive and determination, or you would not have been able to go the the gym day to day. With that mind set you will overcome this, just don't give in, you wouldn't give in on your 3rd set of reps with your biceps, don't let this beat you, you are stronger than this and will get through it. With the different techniques you can do while working out maybe you will find something, that isn't hard on the tendons. Stay strong of mind and heart and I know you will get through this and come out a winner.