Your wife had sex with other people before you, and if something happened to you, she would have sex with new people. So what's wrong with her (and you) enjoying sex with someone else while you two are together?
The only thing you two need to agree on is to try it several times (hardly any activity, riding a bike, skiing, is fun the first time) and if you both can't agree to continue, then stop. No blaming, no recriminations, just stop and move on to the next adventure: hang gliding, scuba diving.