I think another major factor that drove for Kissgate to happen was Faye's attitude towards Aaron after their date. Once Aaron had declared his feelings to Faye, she still seemed undecided between him and Jay. There was also her regular teasing of Aaron about him possibly being bisexual, and her offering to help him out with the ladies, or along 'on his journey', and whatnot. Looking back now, it would seem this behaviour was due to a mixture of her slightly insecure nature, and having seen similar banter once they'd gotten together, it probably was mostly banter.
However, I could see at the time how all this could appear as Faye giving off mixed signals, and possible 'cooling off' her initial interest in Aaron. I get the feeling that Aaron felt as if he was being 'friend-zoned' as a result. Then, of course, there was the night of the kiss with Maisy. There had obviously been a few drinks going around. All three were in bed. Faye decides to get out of bed and specifically asks Aaron to "spoon Maisy". I think, in Aaron's mind, this may have been the final straw with regards to the possibility of Faye actually fancying him. Partly due to his slightly tipsy state, and maybe combined with a slight frustration at the rejection (as he saw it) from Faye, along with "The little one saying she was horny

", he duly obliged to Faye's request, and then added a little on top himself

.
The aftermath of the whole incident obviously uncovered Faye's true feelings for Aaron. He seemed genuinely surprised by her reaction, and as a result seemed to be disappointed in himself at having hurt Faye as it turned out he did. Aaron's explanation to Faye at the time was "It should have been you". We didn't see him explain it to her in any further detail as far as I can remember, and he certainly could have explained it better.. maybe he did and it wasn't shown.
At the end of the day, it did help them get closer as a couple, and maybe have even accelerated the process. It certainly made for a good couple of days viewing!