Try thinking more of him. When you feel the draw to flood the memories by turning to substances and other guys, resist it and instead experience reliving the memories. It is not that you should abstain from using substances or having sex with other guys; you should just abstain from using them as tools of flooding memories. The fastest way to get over him (if it is possible at all) is to think and feel your way through it. If you have other guys, good, though.