Oh Dear...my friends are awkward!!

I must share this story with you all, even though i risk excommunication if i was to get caught, but it's worth it. i was recently out to dinner with my friend and his girlfriend. Their deal in a nutshell; they met at 16 broke up at 17 and rekindled their relationship 9 years later at 26. While i really like these two people, i would prefer to consider them asexual...just an overall awkward mental picture. So anyway, on this particular night at dinner--and-- midway into my wonderful quesadilla, they decide to open up to me about their sex life. And it's not at all what i was expecting to hear. Basically they have constructed a sort of pay scale system if you will. Essentially, each sex act, depending on the time, duration, type etc..will constitute a certain monetary allowance. is this shit even legal? Let me clarify...he pay's her by the way. I wonder how this strikes all of you out there?