Dig up the past. No one likes to dwell upon the conquests of yesterday, but honest discussions can be therapeutic. It might be painful to hear the juicy details about your partner's last love, but chances are, your relationship with him puts his old flames to shame. Getting history out in the open can make you feel better and give you some insight on improving the future. Play by the same rules.
Love is a two-way street, and so is jealousy.
If he tends to be flirtatious, show him that you can measure up. Let your eyes follow the gorgeous waiter across the room, let him know that you have attractive coworkers, too. If nothing else, he'll realize that if he can dish it out, he'll have to take it. Twenty questions will get you nowhere. If your suspicions are unfounded, keep them to yourself.