Don Keefer is in love with Sloan Sabbith.
Right now she's on the other side of the room, hugging Mac tightly and ooh-ing over the other woman's engagement ring. He's just watching her. He can't stop watching her. And at the moment, he's trying to pinpoint the exact moment he feel in love with her.
He knows when he realized he was in love her. It was when that sad excuse for a man posted those pictures of her online. They were sitting on the floor together, and he looked over at her and he just knew. It was the surest he'd ever been of anything. It was exhilarating and terrifying and the only words he could force out of his mouth were "You're impressive", even though he wanted to say so much more than that.
But he's not so sure when it actually happened. The first place his mind goes is that moment, so long ago now, when she caught him completely off guard, telling him the reason she was single was that he had never asked her out. But he's pretty sure that wasn't it. Admittedly, after that happened he had a hard time thinking about anything else, but he was still so wrapped up in trying to make things work with Maggie, trying to be in love with Maggie.
So he also rules out the moment that she finally spoke to him after decreeing that they would never speak again. Something had definitely tugged in his chest, because she was so damn adorable in her awkward embarrassment. When he told her that he'd taken it as a joke (he really hadn't, and even though he was committed to Maggie at that point, he both believed and hoped that he was wrong), the brief flicker of disappointment on her face ignited something inside of him.
In the end, he realizes it wasn't a 'major' moment. He was still reeling a bit from his breakup with Maggie (his office chair could attest to that), and she was just standing in his office, handing Zane his ass for treating her like a stupid child.
And that was it. That moment when she showed how intelligent, strong, and capable she truly was.
He realizes, though, that there were a lot of things that led up to that. The way she took care of Maggie after the break-up, how she stood up to Charlie after her on-air flub, how easily she whooped everyone in fantasy football, even the way she refused to speak to him. She's brilliant and odd and infuriating and adorable and he loves her.
The way his heart swells when she turns her bright, smiling face to him confirms it.