There's also the fact that while Dora and Marten were still dating, Tai told Marten that she wouldn't be able to take his sloppy seconds if they broke up. And, Marten may have told Dora that for whatever reason...
Given that Tai's actually having a more mature viewpoint towards this, them dating actually wouldn't be an awful idea, now. It wouldn't last, and it would count as a rebound for Dora, but what it could do is teach Tai more about what she's looking for - she's clearly put Dora on a pedestal, and them dating would knock Dora clean off that pedestal.
I don't think Tai actually has a problem with Dora being sloppy seconds. That might have been Tai trying to make herself feel better about Dora not being available then. As soon as Marten and Dora broke up, those feelings went away pretty quick.
Whether Dora knows about her comments or not, she did seek Tai out at the party. She could have gone home after the date.
And your right. Being in a relationship with
anyone usually knocks them off any pedastals on which they might have been placed.
I don't really know whether Tai and Dora would be a good match. And neither do they (whatever that means for fictional characters.) There's really only one way to find that out, and that's to give it a try.
It seems like Dora knows (finally!) that now is not a good time to try something like that, and if she did it would just be doomed to failure. But she's trying preserve the possibility for the future.
Either that, or she's completely oblivious to everything, which is still a possibility.
At least now, everyone in the gang can hang out and be friends again.