Give him a nice surprise. Fancy depilation of the bikini area, new underwear, or a tender kiss - for no reason, will make that He will not be able to stop thinking about You, for a long time "after" ;-).
Go sometimes just under his nose, in his shirt or pajamas. Nothing pleases a boy like being aware of his thing. It will be a nice gesture on your part, which he will remember for a long time.
Treat him like a friend. The best foundation of love is friendship and trust. This does not mean that you have to treat him like a buddy. Just be a support for him, make him share his problems with you, show him that no matter what he does - you'll always be on his side. All this will make your luby never think about looking for a new object of sighs. Why, if he has you?