[AhmedFan2004]

It's mainly Marcus jealousy and pride being hurt.

And Noirin feeling guilty about lking Tom, plus angry that she looked silly/2-faced.

Tom may turn out to be gameplaying/toying with them, but Marcus and Noirin acted like they did and were so affected by it, it revealed it all.

You don't exclaim that much at 2 am unless you feel very threatened and bothered by it.

With Marcus, that's to do with his alpha male status (lol).
With Noirin, that's to do with guilt and feeling hapless to Tom.

That's the reality. If he turns out to be sneaky, fine, but the true reasons are evident.