We are but given partial information regarding the answer to this question. The chapter you will want to re-read is Chapter 10, when Lorraine and John come clean with Mr. Pignati about their true identity as school kids as opposed to the charity workers they had pretended to be to get to know him. In response, Mr. Pignati reveals to them something that John had already discovered when he rummaged through a few of Mr. Pignati's things upstairs: his beloved wife, Conchetta, is actually dead. He does not give us details of how his wife died, but it is clear that his wife was incredibly important to him. Note what he says about their relationship:
"We loved each other. We didn't need anyone else. She did everything for me. We were each others life," he managed to say, and then broke into sobs.
This of course is a key moment in the development of the relationship between John, Lorraine and Mr. Pignati, for it represents a new level of honesty that comes to characterise their relationship.