Thinking about it a little more, it may also be significant that Lena's train of thoughts on this generally goes "i know i shouldn't but..." rather than "cheating is bad but..." i.e. it reads more like she's acknowledging social norm she "should" conform with and not really something she personally feels all that strong about (when not being on the receiving end, that is)That is pretty much a close description of Lena's personality so far given how she behaves also if you consider the fact that she never consider or ponders on having sex with Ivy as cheating too, that was a bit meh that you would at least consider having sex with Louise "I know I shouldn't do this but..."(as she does with any other character) and when Ivy she doesn't even give a thought to it. What you said is probable.