I think Lyssa already mentioned during the apartment scene (the one for Stacy) the only reason she didn't fucked Mike there was because without lube he would wake up the whole bulding, considering her weapon of mass destruction.
I do think the game is bulding up for some more anal with Lyssa, Dahlia and maybe even Daisy topping Mike.
Because Lydia is a plot device to move the story along.
Also it appears she is more on the ACE spectrum, having little sexual drive when compared to the others and it doesn't help that the little she has seems to come from hearing about Mike's sexual adventures..
So she will likely not to leave his side anytime soon. Personally i find Mike's infatuation over her boring and was happy with the choice to not profess love for her.
Stacy not looking for sex?
By all accounts she is more of a pervert than Mike. Hell i even suspect something happened between her and AmRose considering how intimate they looked when saying goodbye after the party (it is not Mike's job to guard Stacy's pussy).