Cooking halloumi/wet food on stainless steel without sticking
First things first, make sure you're keeping that pan on high while the haloumi is in there... you can get the pan as hot as you want, but the water in that cheese will cool it off right quick. 

Though in my experience, sometimes halloumi just sticks. When I'm cooking something potentially sticky, I always have a nice-quality, even, sharp fish spatula on hand in case I need to save it. If you really put some pressure on it, scraping along the bottom of the pan like you're removing a sticker from a window with a razor blade, you should be able to save your nice sear. As long as you're applying even pressure and using a flat bottomed pan and have a nice quality fish spatula, you 'shouldn't' gouge it... though that's the reason I use heavy commercial steel cookware from companies like Winco, which I could replace pretty easily and cheaply. ;-)