After people have been married for a while, they tend to stop pursuing each other. It feels nice to be thought about, and in marriage we often feel like just part of the scenery. Make an effort to notice your husband and tell him about fond memories of your own relationship. This should spark reciprocal action on his part and bring back some of the passion for each other that gets neglected in day-to-day living.
I don't think reminding your husband of his previous relationships is such a good idea. Especially not at this point. Men's feelings of self-worth are really tied to their sense of sexual prowess, so opening that door now could lead to a cheating incident on his part.
As far as what to say to him, just tell him that it's nice to be considered and that you feel as though the two of you need to make a better collective effort to make each other feel that way. Apologize for reliving your sexual history with your ex, and maybe adjust your work-out schedule so as not to bump into the ex at the gym anymore.

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