All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
This condition described in the question is normal, and many people are like that, so you are not obliged to inform the fiancée about it and you are not sinful for concealing this matter.
Allaah Knows best.