You need more help than I can give you. You need to learn that you shouldn't have to manipulate your feelings for other people, and that you aren't responsible for their actions.
Find a therapist that can help you get your self-esteem back and help you learn to be yourself. You can't look at others and know what they are thinking or blame yourself for problems that they are going through.
You have taken the first step by admitting that you have problems. The next step is getting help for yourself. Loving people does not cause depression and you will learn that with help. When you learn to love and accept yourself for what you are, you will be able to love and care for others without the guilt.