The key is to make her feel very secure in the relationship, to explain why you find it hot and to keep consistently demonstrating that it turns you on during sex - things like allowing her to see you get hard while she talks about it or takes the dildo while you role-play it being another man. Important thing is to "cuddle" her after you have sex like that, to show you're still into it after you cum and make her feel rewarded by the experience / reduce any shame or uncertainty she may feel afterwards.
As said above, small steps may be key - maybe take her to a club and, after getting her worked up a bit, tell you want to watch her dance with someone. That will be a soft step that gives you an opportunity to show her how it turns you on and prove that you won't have a negative reaction.
You also have to explain that you're not with her because she's some chaste virgin but, quite the opposite, her sexual adventurousness is part of what makes her attractive to you and something you're looking for in the girl you'd marry.
If you wait some years to do this and the relationship deepens, you get engaged, it is only going to make the stakes higher for her, in terms of worrying about how it could change your perception of her or affect the relationship.
Looking back, if I had been secure enough to try sharing early on, I think it would have been a lot easier to make happen than it is now after marriage and kids.
Well, first of all a good advice.
My future HW discovered already before our marriage that it was very difficult to make me jealous.
On the contrary, I liked her getting attention from other guys and she was enjoying it fully.
Especially during I was student at an university.
I didn't know the expression cuckold at that time but I can assure you there were events I was.
I don't say there happened nothing during our marriage, but it took some five decades she confessed dreaming of being shared.
We decided to discover.
Now we both regret that we didn't start much earlier with this lifestyle.
A good communication is a must. What helps a lot is having a very good and happy marriage.
Having 100% trust in each other is perhaps a must. Being complete honest to each other.
If a wife knows that her husband don't leave her because other men can have pleasure with her, no, he encourages her, not much problems will arise.
All of this is no guaranty that a marriage will last forever. Both must be aware of this.
And even the rule we made, that if she would fall in love with another men and this would affect our marriage she would cut this relationship, isn't a guaranty.
Once, she fell in love with another man but it our marriage didn't suffer from it.
I may say on the contrary because she could tell me details or her sexual fantasies with him. We loved these pillow talks.
I sounds strange but we became even closer by this.
FOR US IT WORKED PERFECTLY.