It sounds like you're destroying your chances at happiness because of excessive anxiety about being cheated on--so you've pushed him into "playing the field." Have you discussed fully how frightened you are and scarred from your past experience? How long has it been since your divorce? And how many post-divorce relationships have you had? and for how long each?
How long have you been seeing this new man? If you are past the 3-4 month early infatuation stage, it would be very normal for you to ask for an exclusive-dating agreement with your manfriend. And if you still found yourself paralyzed with fear of deepening your own commitment, then the best way to prove your love for your man would be to engage in weekly personal therapy by yourself (with the option of inviting him for some sessions) in order to work out your inner resistance to trusting another man after what happened in your marriage. For you need to dissolve this deal-breakinbg barrier within yourself, even if you end up not being ready for marriage, or discovering that your new love isn't as compatible or reliable as you now think (because you're losing it).
As soon as you make YOUR commitment to dealing with your distrust (and whatever else may be connected to it), you can ask your manfriend to commit to exclusive dating with you--even though it's possible you have blown that chance by allowing him to get excited about a new possible girlfriend.
Because you've let this "open-door-policy" go this far, I'd advise you to tell him you WANT him to refrain from dating anyone else for at least 1 month while you dive into your own therapy to make yourself more ready. But don't make it an absolute condition, because you seem to be suddenly changing your mind, so you'll need to let him know you don't have the right to insist that he change his attitudes just as quickly as you have changed yours.
PS. If you're only 6months separated from your previous husband, you're inner emotional being is probably not ready to commit to marriage again, though you could fall in love (that's called a "healing relationship"). In the first year after a divorce, it's common for women (and men) to dive into a new love, because it feels SO good and esp restores their sense of being the person they knew and trusted from before in their marriage. But in 3-6 months they can discover that they're not tuned in with the "whole person" of their new love yet, and there are unrecognized parts of him that are alien and even off-putting.