The 2nd last episode "Will is Home Alone" always felt like a filler episode to me before the finale.
In series 3, they did the arc with Tara and Simon's relationship lasting most of the series and it of course ending in a humiliating fashion.
Then in the next episode, it isn't acknowledged at all. Simon is only focused on wanting to go golfing with his Dad. None of the boys take the piss out of him for and Carli doesn't appear at all. She knows Simon is very much into her and to some extent she's in to him as well. It would have been interesting to see what she thought about him actually getting a serious girlfriend that isn't her. Their relationship is the main thing in the finale.
I think they should have included both of the girls in the episode. Have Tara show up in the common room, stare down Simon, give him a disgusted look and then leave. Jay could then make a joke about it. Later in the episode, Carli could have spoken to him and asked what he was up to/who he was dating and rekindle his feelings for her for the finale.
The rest of the episode could have been the same.
I know the show is focused more on comedy than narrative but I think these 2 simple scenes would have set the finale up better and connected the 2nd last episode with it better.