"I have finished the first chapters of how to prove it, foundations of computer science and algorithms book. Although I am interested, I find myself lacking the motivation to continue...And this adds up, days to weeks and then months. Then the cumulative depression rides me to hell. "
It seems to me that you may be overloading yourself, especially if you have a 9 to 5 job. One of my friends is working through "How to Prove it" (see http://technotes-himanshu.blogspot.com/search/label/htpi for his blog on his progress - just one book, not three books like you are doing ). He has a boring (but consuming) corporate job, just got married and is other wise busy. He works for a steady 4-6 hours or so every Saturday and that is it.
And from personal experience, if you are trying to "level up" technically on top of a demanding work schedule, a steady and regular series of small bites seems to work better than ultra intense efforts, which burn you out fast.
PS: If your algorithms book is CLRS that is a tough book to combine with other hard books and on top of a job!