If sex is explosive between you two, it stimulates and "etches" a little area of his brain. You know the sensitive areas that can do this. If it's ho-hum sex, it's probably forgotten in 10 minutes.
If you have a little sign, wink, twinkle, taste, mannerism, tease or a fragrance associated with it,( the more senses you can stimulate, the better;vision, taste, smell, hearing, touch) that memory comes right back each time with that little stimulus..... a man doesn't only remember that day or night, it can be for a very long time! During the time afterward, as the sex organs replenish themselves,and there is a tingling or chance of an erection, he is usually reminded of that special moment.
Most importantly, it is the mental connection that should be part of sex, that provides the SECURITY that all us guys need and it becomes the total package....after all, we guys are nothing but older, immature little boys who need the love and comfort of a good woman ( mother image).... Men are visually stimulated by woman, so that security part that BONDS you two together even if he finds that new secretary with the large breasts and shapely legs visually stimulating, he knows that he has security, warmth, and super great sex with you that can't be duplicated anywhere.... so he hopefully thinks of you.