Well 5k is quite a lot of money..At the other hand being experiencing this at this age is pretty big and not in a good way.. I got chills when i read about the knife!
At the past i had sex for money i remember once i got paid 2–hunder dollars to get a bj from a married guy. i mean guys would suck his dick for free so i got 200bonus. that was alright!
It can be exciting but in a relationship it is dangerous, maybe the third wants it more often or wants one of the couple to be his boyfriend or something like it.