I absolutely think Luke's relationship with Nicole was a "I-have-nothing-better-to-do" kind of situation. I never liked her, and didn't think she was his type at all. Luke's ex-girlfriend Rachel was so spirited, as is Lorelai who we all knew he was in love with, so why he would fall for a dull as rocks, stick-up-her-butt woman like Nicole was just beyond me. I think that part of it was because he was lonely, but another reason could have been to prove to Jess that he was not lovesick over Lorelai, as Jess implied in
One's Got Class and the Other One Dyes (season 3):
JESS: Hey, the girls that I like don’t give a damn about me! And unlike some other people I know, I’m not gonna sit around hoping that they change their minds and suddenly notice me.
LUKE: What’s that supposed to mean?
JESS: You fixed any neighbor’s porches lately? Or you go on a picnic or you get rooked into giving a ridiculous speech at a high school?
LUKE: Shut up.
JESS: At least I’ve got a little self-esteem.
LUKE: Shut up.
JESS: I’m not playing Golden Retriever, hoping one day she’ll turn around and fall in my arms. If she doesn’t wanna be with me, then fine.
And later on that season is when he meets Nicole, and then Jess teases him about how they were flirting, so I think he definitely influenced Luke.
By the way, who is Tyler?
That was probably just a mistake. There was Chris, Max, Alex, Jason/Digger, and then Luke. In between those she went out with that guy from her business class, Paul, and the guy she met at the auction, Peyton Sanders, but there was never a "Tyler".