Time and facts.

Don't push it. If she's okay with you dating, date and enjoy. Don't push anything else.

If you're right, and your wife's feelings are based solely on fear that every woman is your ex, then I think you can probably work around that with time. I'm pretty sure your ex was a far cry from "typical", so it shouldn't be difficult to provide counter-examples--have your wife meet random poly women you aren't interested in romantically.

If your wife doesn't want you to have a committed relationship with another woman, was never happy about it in the first place, and ended up having one bad experience that lasted as long as yours did, it's unlikely she'll be thrilled about you having a committed relationship with another woman in the future.If the problem is more the relationship style, and the idea of you finding intensity in a long-term relationship again, then she'll probably remain reticent about meeting a new love of your life. Possible, but unlikely. You can wear her down, you can figure out a compromise, but she likely won't be be happy about you finding love again. On the other hand, she has no right to control whether you do or not, regardless of her status as your wife. She can let you know her feelings, she has a right to her feelings, but if her feelings conflict strongly with your desires, you get to make the decision about how to honor each. In that case, be honest with her and with yourself that you are making a decision. Don't pretend that everyone is going to end up getting what they want--that way lies madness.

tangent: I would really take that whole "not really a poly relationship" thing with a grain of salt. You were in two committed romantic relationships with two people for several years. Whether your relationships are successful or not is a different matter than whether they are poly or not. I'm bothered by "experts" who decide other people's relationships don't meet the criteria, just because the participants weren't on good behavior. It's white-washing.