When Andrew starts freaking out about the lie he's told and how it will affect Gammy, Margaret actually tries to genuinely comfort him. When she notices how much she cares, it starts to freak her out, signaling that something in their relationship has changed.
Gammy's present to Margaret, made especially touching since Margaret hasn't had any semblance of family since her parents passed away.
When Margaret finally cracks and confesses to what she made Andrew do at the wedding.
Andrew's angry, frustrated rant about Margaret leaving instead of going through with the wedding is strangely sweet in its own way.
Especially because instead of slipping into a BSOD, he followed her back to the company, and upon hearing her telling him why he should just not bother he promptly tells her (quite loudly) to shut up for a minute so he can say his bit and tell her how he feels.