Don't be afraid about your teenage son. He doesn't understand much because he is still immature.
Sons usually love their Moms so much that they don't care even if they turn for prostitution. At least i don't.
Wait few more years until your son is mature enough, and when he is ready to leave home, you can settle down with your cousin.
I am new to this forum because I am also newly fallen in love with my second cousin, I'm male, 24, she is 20 girl. I haven't shared my feelings to her yet. Anyway,
I wish you all the best.
Lord give me strength to break the ice.