ok I'll try to answer in a polite way.
People (even married people) experience physical attraction - that is a fact of life. It is not weird to have a physical reaction to somebody.
However you (as a married woman) have a professional relationship with this ... I'll be generous and call him a young man although I really want to say boy.
Young Man
He is your child's instructor. It is a business relationship and he deserves to be treated as such ... a business relationship. Making up pet cutsey sexually charged names for him and actually using them oversteps the boundaries of that relationship.
What you are doing is not all that different than an older man getting his jollies peering down the blouse of a teen waitress and and calling her his little sweet thing. It comes dangerously close to crossing the line toward sexual harassment. He is at his JOB and he should not be put into the position of having to defend himself from what is very likely unwanted familiarity.
And that does not even begin to address why your husband is giving you a look over it ... even though he is just fine with his adulteress wife panting after other men in his presence. right.