I don’t fall into that category of women but I will try my best at answering.
Guys lure women in such a fasionable manner that it’s so hard to tell whether he is actually sincere to her.
However, in my case the ‘other girl’ didn’t even know about me. Guys are so good at concealing the truth (well for a short period only since eventually they get found out).
Hope that answers it to some extent.
Off to get some much needed sleep right now!
-Sama