If libido is not type related then why would cheating/fidelity be type related? It seems that it is easy to say that SJ's will not cheat..... Would a person not cheat to have sex?? Would this cheating at least some of the time not be related to satisfying the libido? Would you trust an ISFJ male more than an ESTP male with your date if she looked like Charlize Theron and they were alone together??
Especially in the cheating case, I think that it isn't really a crave for more sex (high libido) but instead the fantasy of having sex 'behind their partner's back'. With fidelity, the person may feel more comfortable having sex with their partner thus filling a sexual desire of sorts. This is what makes them type related, as with cheating a person that loves to take risks may get a 'buzz' out of that, whilst a more conservative person finds comfort in the concept of fidelity.
Peguy has done a good job here of revealing one pre-supposition after another. It's odd how many narrow assumptions you have. It's actually pretty ironic... The people who seem to represent sexual liberalism... being dismissive of other sexual practices.
Boring is boring.
I'm sure boring people find other boring people interesting, but non-boring people don't.
In conclusion, if you suck in bed, stick with other people that suck in bed.