No, not only:
Python:
# mike
if lena_mike_sex:
# dating
if lena_mike_dating:
// ...
menu:
"You should've asked me first":
// ...
v "It's not like I was planning it! He invited me to check out his home studio and it just happened."
// ...
# no dating
else:
// ...
v "It's not like I was planning it! He invited me to check out his home studio and it just happened."
Ivy will say the same line no matter if Lena has feelings for Mike or not. In fact, neither branch is limited to "love" specifically, it's enough if Lena has slept with Mike, even once, or casually a few times ("dating")
My point regarding this was that this isn't any real indication that it did not happen [on other paths] It simply doesn't get brought up and discussed if Lena doesn't have personal interest in finding out if Ivy and Mike fucked or not. But considering Ivy is acting in the identical manner in both scenarios, it's reasonable to presume her other actions with Mike were also identical, i.e. she's fucked him no matter if Lena has also slept with him or not.