It was Marz. The Kyle/Donna relationship was actually developed quite nicely. They meet when Kyle joins the NEW New Teen?/Team Titans (In Tales of the NEW New Teen?/Team Titans Spotlight Quarterly #117 or so). The next week, Donna helps Kyle move into his apartment (he'd just moved to NY), and while they're talking he finds out she was Wonder Girl.
"Wait... You were Wonder Girl?"
"Yes. Why?"
"No... Nothing."
"Come on, tell me."
"It's just that, when I was a kid, I kinda had a crush on Wonder Girl... And it's just that... she looked cute on TV and the papers..."
"Really?"
"Yeah, really."
"And why do you say the Girl WAS cute?"
"B-Because she was... you are..."
"Much better. I like you, Kyle Rayner."
Then they have a couple of dates (one was a walk in Central Park and the other a picnic in Mars), and they kiss in the Christmas issue (when Kyle gets stuck on monitor duty for being the newbie). A while later, after some problems, they broke up and were miserable for some time, until they came back, better than ever. It all seemed very promising... until Marz had to end the relationship abruptly because John Byrne was writing Wonder Woman and he didn't want anyone else using Donna.
The thing with Jade started a while later, when she had lost her powers and was staying with Kyle from some reason (they barely knew each other). During Emerald Knights, when Hal from the past was getting all the attention, Kyle was feeling neglected by superheroes and villains (and possibly readers too). Jade comforted him, and one thing led to another... That's still going on, I think, though it's obvious it's gonna end at some point of the last arc of the current GL series (and possibly Kyle's last arc ever).
