The last time I was with my fiance was July of 2017. Is it okay to apply for a fiance visa at the end of 2019 or would it be wise to visit again at the end of 2019?
You can't apply at the end of 2019. The two-year meeting requirement when you file is extremely strict. In fact, we saw an appeal where a person had gone over by about 28 days. They were over the two year limitation. In other words, it had been basically 25 months, since they'd seen their fiance. They applied, and were denied. They even appealed it and spent all that money to go to the Board of Immigration Appeals. It was still denied.
They are really hard about that rule. If the two year mark is up in June, you will not be accepted if you apply in December. It's not going to happen so you need to apply before June, or if you can't file by June, you need to plan another trip to stay within the requirements. Don't waste your time and money applying beyond the two-year mark, because that's one rule that we've never seen them budge on.
You need concrete evidence that you met. Chat logs aren't going to cut it. You need to show travel documents, a stamp in your passport that you entered the country or they came here, photos together, receipts from restaurants during your trip, etc. That is one thing they don't give any ground on if you can't prove with certainty you have physically been together within 24 months of filing. You will not be approved.