You're asking two different questions.
Personally meeting in the last 2 years is mandatory for the USCIS petition.
Bona fide relationship is proved at the consular phase, after petition approval.
You have no timeline, so you'll need to tell us your beneficiary's country of residence.
Depending on your beneficiary's country of residence, "front-loading" of the USCIS petition is helpful. This means that you'd not only include airline tickets, hotel reservation receipts, copies of passport stamps, et al., but also a few (or more) photos of yourselves together during each visit, and a few (or more) representative letters or texts spanning the time of your relationship.
Avoid (like the plague!) any correspondence in which you playfully refer to yourselves as "husband" or "wife"; these will kill your I-129F petition and certainly any chance at the K-1 visa.
Awaiting your answer regarding the country.