This is a very sad but common occurrence among guys who try to treat women with respect. Females with insecurities in their intelligence, appearance, sexual ability, etc. need constant praise and reassurance. Daytime boyfriend's fill this need by showering these soulless leeches with the praise necessary for them to make it through the day. This praise is usually genuine, but its affect is in vain, as the cavernous void which are these females just grows larger. These well-meaning men never actually date the girls. The tramps are very adept at leading them along enough to continue the praise and adoration of their worshiper, without any actual reciprocation (sexual, or otherwise). Thus, the men are boyfriends during the day, hearing all the inane problems of these women and helping them cope with their gnawing lack of self-worth, and at night go home with their dick in their hand.
The only real cure is from a change in the male's behavior, seeing as how these exploitative females see nothing wrong with their platonic relationship. He must let his nuts drop and cease being a total bitch. A creative way to ruin this girl to any infatuated guy is to picture her wincing in the pain of constipation, and then letting loose a fudge dragon. You are welcome. (Note: This has been learned from experience.)
If you can't think of an example from the above definition, you are or will soon be a daytime boyfriend.