Finding purpose in life is a life long task.

As you age, you find that your purpose and expectations will change. Sometime when the changes are unexpected, it can cause depression as you are feeling now.

The KEY to overcoming your depression is to realize that it is a FEELING. The factors around you have not changed. Your parents still love you, you have your gf and your friends. It is only your PERCEPTION of them that has changed.

Why do people get these feelings?

if I have the definite answer I will be more famous than Sigmund Freud.

But being able to identify that it is actually merely a Feeling gives you the power to exercise your Will not to give in to the Feeling.

Look at it as similar to going on a thrilling ride, take bungee jumping for example.

Fact is, it is quite safe with a very small chance of accidents. But many people will be afraid to do it because of fear of heights etc etc.

Those who do it exercised their Will power to over come their fear and make the jump.

Similarly you can exercise your Will power not to Feel the depression but to divert your attention to other areas of thoughts that will cheer you up. This is especially helpful in the middle of the night when you are alone.

Recognize that depression cannot hurt you unless you allow it to. Paying attention by entertaining depressing thoughts gives it strength while ignoring it and diverting your attention weakens its power over you.

You have done well by being able to talk to your parents and gf.

Take the next step by willfully ignoring the feelings when they strike you.

All the best to you in your studies.