According to this, this, and this, the dating world in Mass Effect 3 is exclusive to a singular person for the duration of the game. In other words, I'm not capable of romancing Ashley and Samantha at the same time. Also, if I put the moves on Liara, even if I later let the air out of our romance balloon, I cannot "reinflate" it with someone else down the line.
This imaginary line between friends-with-benefits and monogamous-lockdown is blurry. (Just like real life!) This leads me to my question: How do you know when you've crossed the line between friends and lovers?
Is there a notifier somewhere in the game that tells you you're exploring new territory? Or does your new belle/beau sparkle with some sort of visual cue? Do the other ex-potential-lovers avoid making eye contact when you pass them in the hall? Is there any way to tell at all?