They have very little interaction in the movie and books, but have some more in the RotG comics (official and unofficial). In the official, Pitch flirted a bit with Toothiana (by calling her fairies "cute" who are Toothiana's extensions of herself). In the unofficial ones written by Rufftoon who was an artist who worked on the movie, Toothiana showed some care about Pitch and when he became too strong, she tried to stop him by words and tried avoiding fight with him.
Tooth and Pitch are polar opposite in appearance and in personality: indeed, Tooth is very colored while Pitch has no color and only is wearing black clothes. While Tooth is sweet, bubbly and very friendly, Pitch is cold, violent and lonely. Nevertheless, they both had suffered loss of their families and are both had been parents at one point (Pitch for his daughter and Tooth for her fairies).
Some scenarios show Tooth looking into Pitch's past through his teeth and wishing to fix was is broken in him, as she punched him into teeth at the ending of movie. Some fans like to attribute the kidnapping of Toothiana's fairies (save for one) as a misguided cry for attention and affection from Tooth. Their relationship could be dark but passionate.
Note: Please add only ones that are part of the RotBTD fandom