Hello- Thank you for asking the question. I have over 30 years of experience working with individuals, couples and families & am happy to reply.
It sounds like your son is exploring with sexual fantasies that he has learned from some venue- most likely the internet.
This is age where young males are having all types of sexual urges and fantasies and although this may appear bizarre to you- from what you write, I do not see anything that is particularly abnormal in terms of what teenagers do when curious about sexuality.
As you will see in the following link that addresses Adolescent Sexual Curiosity- this is an age o of curiosity and experimentation.
If possible, this is an opportunity for you to broach the subject of sexual curiosity (which is normal for children of this age) with you son. Proceed with a non judgmental approach and he is likely to be more open and honest with you and through this process- strengthen your relationship.
If you have additional questions, please respond, I am happy to help.
Otherwise, I wish you the very best.
I appreciate your positive rating so that I receive credit for my time.