what about the episode of the anime where lenalee went shopping to get a present for her brother and allen was staring at her and lavi comes over and says something about allen staring at her??? i always assumed that was a filler episode due to the lack of meaningful content, but could it be that something like that was also in the manga?
No, your first guess was right, that was a complete filler episode. I don't remember that scene, but it probably is there.
If Nea had a "something" with Road, how much weird could be an AllenxRoad?
I guess it would be hard proof that even though Noahs as a group and individually consider each other siblings, they could still be in a romance. Which if you think about it we already knew, since the original Noahs repopulated the Earth together. And Road definitely seems to want a romance with Allen while knowing that he's got a Noah memory....And maybe Sherril wants one with Road, in a way. Man got very jealous about the suggestion Road has a history with Nea.
Other than that, unless the theories about Allen being a de-aged and amnesiac Nea are true, which they might be, Nea's not the same person as Allen even if they are are in the same body, and so the viability or not of Nea/Road doesn't affect that of Road/Allen. Although...no, it probably does, because if Nea/Road turns out to be canon, it's increases the chances that Road's feelings for Allen are actually her feelings for Nea.
i must say when road kissed allen there was a healthy saliva trail between their lips, and lenalee did seem AWFULLY jealous
That must be a difference between the anime and manga. In the manga there isn't any saliva trail - not that a saliva trail means anything in particular - and Lenalee didn't act jealous. (Actually, her reaction at the time in the manga isn't shown.)
But! In Gray Ark, there's a section on mission reports. Lenalee writes the part of the report taking place in that room, and she does comment on the kiss.
Allen entered the tower, and is greeted by Road’s kiss! What went on between the two of them since the incident in Rewinding Town?
Is that jealous or not? I tend to think it is, but it could be interpreted either way. It's quite a change in behaviour from the last time Road met Allen, so a person would wonder if anything happened between those times, though we as readers know nothing did.