Ideally you should spend a bit less time than that if you can. The rule of thumb is to spend 2x as much time outside of the US than in the US. So, if your previous visit was 30 days, you should spend at least 60 days out of the US before trying to reenter. If you're visiting for 80 days, that means after it, I would not even try to visit for the next 6-9 months, maybe even a year.
80 days is a long visit, even on B-1 / B-2 visa, let alone ESTA.
Don't forget, relationship is a two way street. Your fiance can visit you in Europe too and enjoy some things that don't exist in the US.