"it was an evening.... when no one was near." What are your thoughts and feelings as you read the text?Its how we feel about the relation between the son and the mother
If we knew the specific text from which you have taken this quote, it would help in analyzing the relationship being reflected. As with most relationships, the information conveyed in the quote probably carries different meanings under various circumstances.
There are times when it's wonderful to have some quiet solitude at the end of the day. The opportunity to reflect on the day's activities in peace can be a treasured part of the routine for some individuals. If this is the case for your mother and son, the quote may simply indicate that they were comfortable allowing each other time and space for themselves.
If "no one was near" because one of your characters is living in a situation of isolation or estrangement from society, the alone time becomes much less positive. If the mother and son are physically or mentally distanced to the point of destroying the relationship, then the quote is a sad commentary on their relationship.