HPL's family fortune declined sharply after his childhood. He was raised by his mother and an aunt, as his father died early in his life. They owned the home, with a scanty inheritance, but that was about it. He married for a few years in his thirties and lived with his wife in New York, but when they seperated he returned to Providence.
When his regular magazine changed ownership, the new publisher didn't like him much at all, and he rarely got anything published in his own name. He turned to doing edits and re-writes of other people's work and out and out ghostwriting to survive.
Much more prolific than his fiction are the long-term and varied correspondences with other writers who became known as the Lovecraft Circle. This included August Derleth among others
"At the time of his birth Lovecraft's family was quite well-to-do, most of the wealth derived from the extensive business interests of Lovecraft's maternal grandfather, Whipple Van Buren Phillips. This prosperity, however, was not to last. The death of Whipple Phillips in 1904 had two calamitous effects: it robbed Lovecraft of one of his major early influences (for with the death of Lovecraft's father in 1898 of paresis the raising of the lad had been entrusted to his mother, his two aunts, and especially his grandfather); moreover, because of the mismanagement of affairs by Phillips's business associates, Phillips's fortune was squandered and the Lovecrafts were forced to move out of their palatial mansion. "
S. T. Joshi
http://www.themodernword.com/scriptorium/lovecraft.html
I recommend Joshi as perhaps the most competent biographer of an enigmatic man.
Regards,
Scott