It's about Sherlock. Of course it's about Sherlock. It's always about Sherlock, it's always been about Sherlock and it will always be about Sherlock.
Molly's feelings towards Sherlock have never been a secret, nor has his growing respect for her, which Greg does not like one bit. He especially doesn't like the way Sherlock kisses her cheek after a longer-than-a-high-functioning-sociopath-is-able-to-bear hug. It doesn't take long for Molly to notice how much of a huff he's in. When she asks the answer takes her by shock.
"Are you kidding?" she asks. "You seriously think I still fancy Sherlock?"
That's exactly what he thinks. She's fancied the pants off him for years and only started officially dating Greg three months ago. He is not interested in being a rebound for anyone, least of all after what relationship hell he's gone through in the past.
But he is not a rebound and she is not his ex-wife. He is her boyfriend and for a good reason. When she tells him this she's ranting at the top of her lungs and doesn't care if his colleagues outside his office are staring, making faces or chewing popcorn. All she cares about is getting it through his thick skull that she loves him and that she will never betray him for someone who doesn't see her in the way she used to.
Greg feels his breath catch and pulse jump. For a moment he's speechless and stares at his now silent and slightly tearful girlfriend.
"You love me?"
She nods.
"Of course I do. I've never felt this way about anyone."
He has, though. He felt this way about his ex-wife and she broke his heart. Then again, Molly is not his ex-wife.
"I love you, too."
They very quickly learn the importance of make-up sex.