After reading about the new episode, and the new promo (I have seen neither), I'm going to try and somehow make sense of all of the confusion going around. I'm going to (try) and keep calm whilst writing this, but no promises there.
From what I've heard of the episode, it seems to me that the relationship right now is largely one-sided; this time on Lindsay's side. She seems to take their 'relationship' (as we do not know the state) more seriously that Danny does. She's upset that he forgot her birthday, okay she's mad but who wouldn't be if someone you cared about forgot your birthday? Danny has a good point, he's not good at remembering birthdays (nor am I for that matter) so I'll let him off for that one. By what people have said, it seems Danny doesn't realise she's upset - maybe, but I haven't seen it so I don't know. Emotions can be hard to judge, and perhaps I see differently.
End of episode.
The promo shows Danny kissing 'someone', I'm not naming who yet, because we're not sure. We see Lindsay telling him she's fallen in love with him, he looks shocked. (Again, no idea, playing off what people have written and said). Two conflicting stories: Danny/Rikki & Danny/Lindsay (if Rikki is infact the one he was kissing).
This is the only theory I can conjure up without resorting to any cheating.
From the differences between Danny and Lindsay in the episode, I seem to think that their relationship after Snow Day wasn't serious. They did, they enjoyed themselves, but they didn't take their relationship further but remained good friends. Lindsay, now seems to be the one who's more invested in the relationship. Danny doesn't seem so....eager. But that doesn't tell us what he's feeling.
My thoughts are that his and Rikki's fling (if it happens, that's what it's going to be) does something to him, and he's not prepared to hear Lindsay tell him she's fallen in love with him. He's shocked perhaps because he's realised he's in love with her too, but what he's done with Rikki can't be forgotten. He tells her what he's done, we get a flashback of what happened between them (Ausiello said possibly sex involved, doesn't mean they did it) and left with Lindsay trying to absorb it all in. She gives her monologue and by the end, they decide to take it slow, but embark on an exclusive relationship. Lindsay can't harbour any ill feelings because she never told him how she felt about him, and maybe we get Danny repeating the L word to her too.
If what I said even remotely makes any sense, by future episodes, Rikki no longer exist, and Danny and Lindsay are in a slow, but loving relationship together, which can be seen by 4x19. They've cleared the air, and are happy. 4x20 stuff bugs me slightly, but I can only imagine that Danny might have pulled away slightly, out of guilt of how he's hurt her, even though she doesn't admit it.
By season 5, they're happier together and hopefully the lime light shifts to other members of the cast, leaving Danny and Lindsay's relationship still going strong but not a large sideplot of the season.
If that all happens, I can live with it. Danny's grief is bound to get him in trouble somehow, and a possible fling of confusion does happen. It's not a relationship, it's a small fling (or just a kiss). Nothing big to it. Pam Veasey and Anthony Zuiker have said that they're in love, and what we've seen so far isn't it. So maybe, this just pushes them up to that state of their relationship. It's certainly more than a bump, but I can't see it as something Danny and Lindsay can't work through.
I refuse to give up on this ship yet. DL is half my life and refuse to watch it go down the drain because of the faulf of some pompous writer deciding more drama would increase ratings. I'd frekin' boycott the show and teach them a lesson about messing with their fans. When you've built up a loyal fanbase, you don't go and destroy it hoping to make it larger. You'd have to be a mental idiot, and I'm pretty sure TPTB has brains - somewhat.