Can I spend the night at my fiance's house once in a while? My fiance lives with his parents because it is not very close.

If your fiance's parents don't mind welcoming you, you can live there, especially if you plan to live with your in-laws after marriage. It is also good to adapt in advance. If his parents care about this matter with a special tradition, especially if they like you very much, because you often live in the past, so that his parents think that you can't live without their son and then despise you, it will not be worth the candle!