Don't panic Seddiers. The last kiss thing is ironic because they kissed again at the very end, after they said they'd break up at midnight.
To be honest the Seddie arc did a lot for us.
1. It proved that Freddie loved Sam. He said he loved her and Creddiers can't really claim he meant it in a sisterly or friendly way because they kissed twice afterwards.
2. It made Sam's feelings for Freddie undeniable. They were first shown in the episode iSpeed Date though, but some still denied them.
3. Mrs. Benson wasn't able to break them up, and neither was the worst thing Sam had ever done to Freddie.
4. Sam and Freddie love each other. They didn't want to break up, but felt like they were trying too hard. Freddie said he loved Sam, and the thing keeping them apart is their differences. All the couples Dan made endgame tried to be together but couldn't for some reason. Examples:
Zoey couldn't date Chase because he was in England and the long-distance relationhip thing wasn't working.
Holly couldn't date Vince in What I like about you because he was a player and she didn't think she could trust him.
Josh and Mindy broke up over an argument and got back together in the end.
And last but not least Logan and Quin's relationship problem was they were trying to keep it a secret.
The Seddie arc did bad things for Creddiers.
1. It proved that Carly would not have a problem with Sam and Freddie being together. Although Creddie fans will deny this, when push came to shove Carly was the one who tried to bring them together. Carly was the one who took calls from people saying Sam wasn't crazy for loving Freddie. When Carly was jealous is wasn't of Sam, but of both of them. Carly couldn't take breaking them up. Carly tried to get them to spend more time together. If Carly was jealous she wouldn't try to get Sam to spend more time with Freddie, she'd tell Sam to do her own thing and go to Freddie's train club meetings with him instead.
2. Pretty much proved that Freddie was over Carly. Would Freddie date Sam if he still wanted Carly? Would he tell Sam he loved her if he still wanted Carly? If Freddie still wanted Carly it'd be the biggest obstacle of Seddie, but in the Seddie arc which pretty much went over all the imperfections of Seddie, Freddie's feelings for (current or former) Carly were never mentioned.
My thoughts on the break up: I don't really like what the episode might be implying. You have to have similar interests to be with someone? Than again if Seddie broke up for too good of a reason people might not support them getting back together.