When David loses his job and Neil offers it to Tim, he recommends Gareth. They've always had an antagonistic relationship, so seeing Tim doing something nice for Gareth reminds the audience why he's the bigger man in the end.
In the finale of the UK version, when Chris makes fun of David's girlfriend and David tells him to fuck off.
"Never give up."
After David stood up to Finchy and before Tim got with Dawn, we see both David and Tim hanging out with Gareth. Three men who have always rubbed each other the wrong way have decided to make the most of their respective situations and try being friends.
After Dawn leads Tim off, the camera briefly returns to David and Gareth; while the latter looks befuddled as always by the mere implication of sex, David seems to be wearing something of a knowing, happy smile, which makes sense; as Dawn and Tim's former boss, he's probably more than aware of the UST between the pair and, in his own misguided way as considering himself their mentor and friend as well as boss, probably hoped it would work out.