I see the bit where Keira Knightly kisses Andrew Lincoln like a sympathy kiss, to show she understands and that she feels sorry
I see it as a way to give him hope and keep him fixated on her.
Mind you, I loathe Kiera Knightly who justs hangs her mouth open to a greater or lesser extent to suggest emotion.
The best man character perhaps felt guilty about fancying his friend's fiancee, so organised the OTT display at the wedding.
When he tries to stay away from her, KK's character turns up, with pie (sooo cute... yuk!) and alone. Presumably, her husband still sees his friend - she could turn up unexpectedly then to meet him.
Then she points out that (and I always hear this in a soppy little voice) "I look quite pretty, don't I?".
Just in case you hadn't noticed, man who patently fancies me.
Eventually, he decides to try to make peace with his feelings, goes to her house to do the stupid card thing and she lets him go, hoping he'll obtain closure...
Oh no. Of course not.
She runs out and snogs him, then skippetty-skips back to unwitting husband (who, some might feel, she's justed cheated on) pleased to have kept poor old AL's character dangling.
No, of course I'm not given to over-thinking 