Upvote:3
There is no rule that having had a K-1 visa will preventing you from visiting on the Visa Waiver Program or using an existing ESTA if you have one (I don't believe your answers to any of the questions on the ESTA would have changed by your having being petitioned as a fiancée and having gotten a K-1 visa).
However, having a US-citizen fiancé raises questions about immigrant intent; and more so in your case because you guys had gone through the whole process of getting a fiancé visa, which demonstrates that you very recently had serious intent to immigrate to the US. So the burden of proof that you are not going to use this trip to immigrate to the US is going to be higher. It would be so easy for you to, after entering the US, decide to marry your fiancé and then apply for Adjustment of Status in the US. So be prepared to face scrutiny about that from the immigration officer.