The sites that Karen posted for you are really great. I am slowly working through the CBT site.
You cannot cause other peoples depression so please don't put that burden on your shoulders.
Just keep talking to us and trust your friend to follow through on helping you.
Raise your head up high and know you are a good person.
Write a list of all the good things about you and in your life.........just brainstorm. Write what ever pops into your mind and then look at it and know you have many wonderful traits.
A Journey of a 1000 miles starts with a single step.