Janice and Floyd are a couple indeed. Maybe they just don't like showing off their relationship too much in public (They don't like going too lovey dovey in public). The only moments I noticed are:
*Their hug during the credits of The Muppet Movie. (And also in the beginning when Janice asks Floyd to buy popcorn for them.)
*Floyd kissing Janice on the cheek in The Muppets Go To Movies
*They've sat next to each other on certain occasions. (They're next to each during "The Rainbow Connection Finale" in The Muppet Movie; They share a bike and sing a lyric together during "Couldn't We Ride" and (if you look close enough) are sitting next to each other on the plane in The Great Muppet Caper; they sit next to each other (and glance at each other (if you look close enough) when Kermit says "I do") at the wedding, their lockers are next to each other, and Floyd defends Janice after Gonzo "yells at her" in The Muppets Take Manhattan)
*Floyd brought Janice up to Statler and Waldorf's balcony in the Danny Kaye episode.
*Floyd is walking next to Janice while telling his joke after "Don't Blame The Dynamite" in the Dom Deluise episode (In the same episode, after "We Got Us," he goes down to her.)
*Floyd and Janice do dance together in only ONE "At The Dance" sketch (In the Pearl Bailey episode. Two other "kinda" moments happen this episode. Janice is Floyd's princess in the jousting scene. Before they sing "In The Good Old Summertime" Floyd mentions to Pearl that "his main squeeze" got him the outfit he wore in the scene (You'd think automatically it's Janice.)
*Other than "Act Naturally," their only duet in The Muppet Show was "50 Ways To Leave Your Lover" in the Paul Simon episode.
* Floyd: C'mon, mama, you know what they say. The show must go on.
Animal: GO ON! GO ON!
Janice: Yeah, but it'll be rul hard to go when we're all dead.
Animal: DEAD! DEAD!
Janice: Oooooh. Please. I'd rather rehearse than listen to that.
(Liza Minelli episode)