It almost looks like a weird love triangle between mother, son and step-father. The son is looking for parental affection and he shouldn't confuse it with sex: (that they both insisted was a father-son affection). And the step-father may just be taking advantage of the whole situation.

Relationships with step-fathers are never very interesting to start with. When they break up with the mother, they disappear (gradually or not).

I'd recommend the love of an independant boy lover. Otherwise this is one big soup of confusion and potentially damaging in the future (and not due to outside interference).