I find "Partners" so fascinating because I like trying to figure out what the fuck was he thinking. Surely he would've realized that Starsky would be completely devastated by that, not just a little scared or guilty? The only explanation I can think of is that he wanted to see Starsky all broken up for some reason. Maybe because he wanted to see how much Starsky loves him; like Ralphie from "A Christmas Story" gleefully fantasizing about how brokenhearted his parents would be if he went blind from soap poisoning.