A friend of mine once said to me, "I don't know what God is, but when I look at a butterfly or a flower, I know that I can't do that." It is possible to view the world this way -- with the acceptance of uncertainty and appreciative curiosity for the mundane -- because of a set of networks in the nervous system that I refer to as the "growth function."
I'm just here to tell you that feeling depressed or lonely is natural and your negative perception of the world is just that, a perception. Everywhere you look there are people who give a damn, so allow them to do so. They aren't psychic and because you're so good at hiding your true feelings, they may never know without your help.
One phrase that gets massively overused is "drinking at something". When life throws you a crap day or a bad situation and we use it as an excuse to drink. Drinking "at" that person, or scenario. Supposedly it's overcome by dealing with our feelings and reactions in a different way. Learning new coping skills.
Maybe it is narcissistic to expect spiritual fulfilment from our jobs. Maybe any quarter-life 'crisis' is only ever a result of adolescent navel-gazing. Maybe we should all just shut up, get on with the task at hand, and learn to distinguish reality from impractical expectations. Or maybe we should question the cultural definition of success.
My daughter finished by saying something that we could all apply to our own lives including in divorce and separation situations and experiences. She said, "Lives are full of accidents Mama and we need to learn from them. It would be really boring if everything was perfect and we had ice cream everyday."
The best way to start reversing your bad habits is to make a series of long term and short term goals which will serve as beacons for the directions of your new habits. For example the most common habit which faces most students is excessive procrastination, in my opinion, the easiest way to overcome procrastination is by setting goals.