Don´t worry, a lot of kids sleep with their parents. This helps to create a strong emotional link parent-child. I guess he still does not start puberty. Have you noticed any physical change in the child or any sexual misconduct toward you?
You and your Fiance need your OWN space as so does the child. He needs and should be sleeping in his own bed.
Kick him out of your bed!!Give him a room for himself.It is a kind of pervert that a 10 year old boy shall sleep with his parents.Do they involve him in the intim moments in bed to???This is sick!!
Bit of a knee-jerk response you had there, I should think - to jump to conclusion that it was sexual deviancy. I'm going to guess that you have some mental health issues that need resolution - might be worth seeing someone professionally about that.