Amber dated Kasey because it was mainly online (I believe), and then she had to move in without a choice, making the relationship longer
Amber dated Krystle because her parents had $$$ and could buy her things/give her $1,000+ allowance
Amber dated Destiny because she felt extremely lonely after Krystle and her broke up/Destiny wanted to cheat
Amber dated Becky because she felt extremely lonely after Destiny and her broke up, needed a new place to live/Becky felt extremely depressed because of her nephew's death
Pretty much it.
Edit:
Letting go of...?
EDIT 2:
Amber allegedly gave a handjob (or was it a blowjob?) in a movie theater before.
As for the "more testosterone=higher libido" being oversimplified, ehhh... This is scientifically based. If you lower the amount of testosterone in anybody, women or men, their libido will likely drop, and if you raise the amount, their libido will likely increase. Sure, there are people with low T and average sex drives, but commonly, it's low t = low libido. It's a big reason why men even get their hormones checked in the first place.
Also, confused. You said that she could keep a guy around sexually, but also that she'd be terrible at it and not do anything fun, and there would be size issues involved, making it more complicated to have sex anyway. A handie isn't going to keep anyone around but a sped, and like you said, he would have a hard time getting around her to hump her.
But yes, she's way easier off finding an insecure girl than guy.
I'm pretty much over talking about this topic because it's getting extremely

fftopic: with speculations and hypotheticals
At the end of the day, Amber seems to only pick people out of convenience.