I never tell one client that I cannot attend his sales convention because I have a previous engagement with another client; successful polygamy depends upon pretending to each spouse that she is the only pebble on your beach.
In displaying the psychology of your characters, minute particulars are essential. God save us from vague generalizations! Be sure not to discuss your hero's state of mind. Make it clear from his actions. Nor is it necessary to portray many main characters. Let two people be the center of gravity in your story: he and she.