Here's my interpretation of the L&L conversation, and the bold parts are what I think they were thinking at the time of the converstation! Some of the things they might have wanted to say but were too stubborn/stupid/incapable to do so. They were thinking these things so the other one never knew what eachother were trying to say.
LORELAI: It really was great of you to come, Luke. It meant a lot to her. (You've been more of a father figure to Rory than anyone and that means a lot to me.)
LUKE: It was fun. (I love Rory like family)
LORELAI: So if I don't see you, have fun on your trip with Nicole. (That other woman who isn't even your type by the way)
LUKE: Oh, we may not go now.
LORELAI: What? You were really looking forward to it.
LUKE: I don't know if the timing's right and. . .things are kinda weird right now. (Because shes not the woman I want to be with...)
LORELAI: Oh no.
LUKE: What?
LORELAI: It's because I teased you about the commitment thing and proposing. I ruined it.
LUKE: No, that's not it. (Yes it is, dont lie to her fool)
LORELAI: Please, promise me that's not it. It would break my heart.
LUKE: But you weren't wrong about that. It got me thinking and it is kind of like committing to her.
LORELAI: So?
LUKE: I don't wanna lead her on. (I dont want to commit to another woman if there is any hope in the world that you feel the same way I do.)
LORELAI: But you like her, Luke. You like her a lot, don't you? (I dont know why you like her, everyone in our stupid town was always trying to tell me how much you liked me, even my mother knew. I was apparently the only one who couldn't see it.)
LUKE: Yeah, she's great. (But shes not you.)
LORELAI: Then go. No matter what she's reading into it. (That's great Lorelai, push him to commit to another woman, really great)
LUKE: Really? You think that's okay considering. . .I don't know. . .everything? (Considering how I've been pining for you for so long but have no way of showing it other than fixing crap around your house, building you things and basically doing everything you've ever asked me to because I'm an idiot and can't just do something about it.)
LORELAI: Yeah, I do. (Yeah sure, go be with another woman, it's not like I ever gave you any indication that I might have feelings for you, so it's not your fault...)
LUKE: Oh, okay. I'll probably go then. (Please please please stop me from going. say something to stop me going)
LORELAI: Good. (Why good, it's not good, don't say good... idiot)
LUKE: I guess I was just nervous about nothing. (and lack of any form of reciprocation of all the feeble attempts to make you realise how I feel...)
LORELAI: That's what I think, too. (Maybe he wasnt as into me as everyone thought. Maybe I'm reading too much into this, maybe it's because I never said anything... I don't know, I don't want luke to be with her... Who would I want luke to be with? Me? .... Am I being selfish? I just want him to be happy... be happy he's found someone.)