Well, I think I realize....
Why you're receiving such negative feedback from everyone, and I can kind of relate with them too.
Well, at first, I watched this episode (eps 5), then I watched 1,2,3, and 4, like you suggested me to do, and then I watched eps 5 again. (I'm just saying this so that you know that I've watched them all, since you suggested people to do so, not in that particular order, but at least I watched them all. :P )
Anyways, here's the problem.
At first, you make it seem like this girl that he falls in love with is very gentle, sweet, and caring. You make it seem like these 2 would be in love with each other no matter what happened. Sure, the guy follows this idea, but in this latest episode you've showed us, the girl turns out to not be this angelic person that she was originally portrayed as. The problem with this is that now everyone thinks she's a filthy whore (.... that being put at the very most, since I felt some serious hate towards her for being such a slut. :P )
However, this isn't the main idea behind this problem. HERE's where the main idea of this problem is.
You now bring up a completely random girl, who had a secret crush on him, and you make the 2 fall in love with each other instantly. Now, I'm quite sure people wouldn't of minded it IF you had emphasized the love the red haired girl had for him. You didn't emphasize this at all throughout the entire series, which is why the randomness of her just kissing our protagonist out of nowhere must of gotten you negative feedback. Sure, you showed us the flashback of her throwing the paperball at her, but that was from the VERY first episode. After that, we're never shown a reference that even relates to the relationship that the redhaired girl had with him at any given point. Sure, you point out that she's considered a friend to him at the very beginning of this episode, but you've made this reference at a very wrong time in this series.
Also, you bring up the guy who got punched in the face earlier in the series, who ends up shooting the random couple. Now I can only think of 3 reasons why he would end up shooting at them. 1) The protagonist stole his friend away from him (the guy who stabbed our protagonist earlier in the series), and therefore he was left to be alone, which caused him to be angry enough to shoot them. 2) He was secretly in love with the red-haired girl, who ended up kissing our protagonist, and therefore, he shoots them. 3) (this one is probably not the reason) He took that punch to the face very seriously, and now wants to shoot him for that..... yeah, that's probably not the reason xD
I think what Newgrounders need is character build up, not randomness. Of course this is just a theory, but I think this is main reason why you're receiving such negative feedback from everyone, and like I said earlier, I can relate to them because I, too, found it to be completely random and unexpected. At this point of the series, such a random event would probably be taken negatively, as it clearly shows in the reviews you've been getting by other Newgrounders.
I think the story is great overall, but I think this episode really dealt it a faulty blow. I hope you get this review so that you can continue on this series for at least ONE more episode. (I'm saying this because you said "The End" at the end of this episode, but I'm REALLY hoping this isn't The End.) You've got to make up for this loss, otherwise, you're series will be shunned upon by anyone who sees it. I'm not trying to say you're a bad flash artist, but for the sake of the viewers who watched your entire series, GIVE IT A PROPER ENDING BEFORE IT'S TOO LATE! lol.
Well, overall, I liked the series to a certain extent, but I'm very sure I'll like it even more(and many others too), if you give it an ending that everyone can enjoy in this series. I'm not saying the ending has to necessarily be a "Happy" ending, but at least fill in all the gaps that you've left in your series. So many unanswered questions is bound to also be a reason for negative feedback.
^_^ Please continue.
- Nondo