Come clean with his parents

The safest path forward for both of you would be for you to disclose your intimacy fantasies with the child's parents. You can frame it as a positive thing, since you felt over the world when he chose you, but if there is a sexual aspect to your fantasies, you need to disclose that too. Better to be "caught" in the planning stage than to let this go any further. You can rest assured that the parents would rather find out now than come home early one evening to find the two of you "cuddling." Your best friends here are transparency and honesty. If you are committed to keeping appropriate boundaries with the boy then tell them that, but if you aren't sure then tell them that and see how they react. In the best case scenario the parents will appreciate your honesty and provide guidance (rules) about how they expect you to act with their son. They most likely will not be ok with any sexual contact between you and their son and any such behavior would very likely result in harsh negative consequences for you and an end to your relationship with this boy, who you obviously enjoy spending time with. If you respect the rules and enforce appropriate boundaries there is no reason this fulfilling relationship can't last many more years to come.