Welcome to the forum!
It's hard to know why he's being cold but I would 1) move on with my life and start dating others; 2) be friendly to him but not engage in small talk; 3) be upbeat in his presence because it will be empowering for you and a mystery to him; 4) use the technique but don't obsess over it. You don't want to be a backup girl, and you deserve more, so either make him step up OR step out. xoxoxoxo