I could easily have written this exact post about a year ago, and in fact I did start a thread titled "Coping with excessive solitude" that touched on some vaguely similar themes.
What you are dealing with in a very stark way in your life right now is something known as "philosophical pessimism". This is a philosophy that was explored and written about primarily by Arthur Schopenhauer, Albert Camus, and Friedrich Nietzsche in the 19th and 20th centuries. It is a fairly bleak view of the condition of human existence, but I can assure you it is not incompatible with finding happiness and peace in one's life.
I'm living proof of this. I find Schopenhauer's philosophical pessimism quite compelling, yet I have been able to reconcile this with an optimism in my own life based on a number of different concepts. First, although I do recognize that all human endeavors ultimately have no intrinsic "meaning", I also recognize that we have to create that sense of meaning and purpose for ourselves somehow. For me, that means staying busy doing things that I know provide both short-term and long-term enjoyment and fulfillment. For example, planning trips. The planning process takes awhile (for longer or more exotic trips) and then the trip itself provides excitement and adventure, etc. Also, I actively seek out and spend time with other people who share my worldview. I have done this over the past year by joining various Meetup groups that have a scientific, skeptical, rational, philosophical theme to them. This way, I can have very interesting, friendly, and fulfilling discussions with people about topics like philosophical pessimism (and lots of other stuff) and can hear their insights about how they are making their way through life.
Ultimately, you have to find a way to make peace with the absurdity of life and just enjoy it moment to moment as best you can. Reading more about philosophical pessimism would be a great place to start, so that you can see there have been some brilliant people who have struggled with and articulated this philosophy over the centuries. That in itself can be very reassuring. Check out the writings of Nietzsche, especially, since his take on the matter was more optimistic than some others.
Philosophical_pessimism (Wikipedia)