Hi, Artemis_Ameretsu! There's actually no particular ending from being a jerk, so you can rest easy and continue treating him nicely. Being mean mostly just affects your interaction with him. As a Valentine special, this game really only has happy endings. Though, someone once mentioned that they wished there was an option to reject the guys, so when I get around to remaking it (likely after I finish Beauty and the War), I'll likely include that choice, as well as an appropriate ending to go with it.