Hello, I'd like to help you with your question.
Depression is characterized by feelings of hopelessness and worthlessness, lack of energy or motivation, thoughts of death and/or suicide and trouble concentrating. It is common to feel there is no hope and no way out. Guilt can be a large part of depression, which may be why your friend is experiencing the thoughts he has around leaving his partner. He feels that he could not cope with the guilt if his leaving somehow affected his son to the point that his son was hurt. It is not logical, but it makes sense if you experience a high level of guilt.
Remind him that he does not have to do this alone. And if he feels better, he can overcome his guilt and live a better life. Keep letting him talk to you, and offer suggests such as help and how he can improve each thought, just as you have been. You can also add
things like asking him about the source of his thoughts. If it was past trauma, you can relate his current thoughts to patterns or responses he learned as a child. A person can change their thought patterns, but only if they are motivated and willing to work through the pain. Hopefully, your friend will consider professional help so he can change his circumstances.
If your friend is willing to see the doctor, then that is a good first step. The doctor may be able to convince him to try a medication so he feels better, enough to try therapy. Therapy is often one of the best ways to feel better. Medications are helpful to deal with the symptoms of depression but they do not get rid of them permanently. Therapy can do that though. To have a better chance at finding a good therapist, try searching on line at http://therapists.psychologytoday.com/rms/.
Medications can also be helpful to ease the symptoms but they do vary in their effectiveness so your friend may need to try a few different ones to see what works for him. Each person has their own body chemistry and what works for one may not work for another. Also, once someone takes medication for a while, the body becomes accustomed to it and the person either needs an increase in dosage or they need to try a new medication. But the medications can help you deal with the symptoms until the therapy begins to help.
Motivation is a very difficult symptom of depression. It often keeps people from helping themselves and reaching out to others. But support and self help are vital in helping your friend overcome depression. Ask him if he will consider support groups, either on line or in person. People who are experiencing the same symptoms as he is can offer invaluable support, ideas and companionship to help him feel better. Also, working on his depression at home can supplement his therapy or other treatment. Here are resources to help him get started:
I hope this has helped you,