This is what Carl Sims said about this.
Patchy will visit for about 5 hours when he does. This gives you time to interact with Patchy in a more meaningful way. Patchy can become a great friend for your Sim While you can Wooohoo Patchy and make him your boyfriend, I had difficulty getting him to move in without cheating. Even at full friendship and romance bars, the option will not come up. If you want Patchy to move in, you might have to do add to family via testing cheats. This should work. Having a baby with Patchy results in a normal human baby, not some cute little straw guy.
http://www.carls-sims-4-guide.com/expansionpacks/seasons/scarecrow.php
