How to tell him without acting such a fool...?

...that I like him, and would like to get to know him better. I'm moving on to another, better job, very soon.... He's been my boss for about 2 years now, I never acted on my attraction to him cos I like to keep things professional at work and partly cos I also thought it was a normal crush (y'know- older, boss etc) and will go away, but no! We struck up a friendship in difficult times at work, he's intelligent, fun, supportive and kind-hearted -and I'm intrigued by him, I can't stop thinking about him and have started acting strange around/ Towards him (either shy, or giggly, or totally paralysed!) and tho I'd normally walk away from such situations with a nice warm buzz and vague questions of "what if...?" I want to challenge myself to acting on this mutual attraction and feeling of fondness... Think he's single, but just don't know how to tell him without coming on too strong or leaving things unsaid. I DO really, deeply, hotly like and desire him...