The most important thing is to be honest if you ARE asked further questions.
Yes, you can say you're on holiday, but if you are asked who you are visiting while on holiday, you need to say it's your fiance, and not just 'a friend'.
A few years ago, I went travelling in South America. I flew to New York, stayed with a friend in New Jersey for a week, then flew to Arkansas to stay with my aunt for a week, before flying to Peru. Six weeks later, I flew back to the US, via New York and stayed with the same friend just for 24 hours while I was waiting for my flight back to the UK (I had booked the flights with different airlines, so wanted to leave enough time to catch the second one in case of a delay).
When I arrived back in the US, I was questioned about how long I was staying, who my friend was, where I knew her from, what her name was and what her address was. Luckily I had my flight information, my friend's address and her details on me. It was a lot of questions just for a quick 1-day stop-off on the way back to the UK, but then again, I suppose only spending 24-hours in the US might have looked suspicious considering I was on my way back from South America. However, I was prepared for questions, had all the information and I was honest, which meant that they stamped me in with no issues at all.