Board Thread:General Discussion/@comment-32181199-20170619135553/@comment-4872828-20170812200614

I thought when "When Worlds Collide" aired it put the coffin nail in the idea of a "triangle."

At the beginning, April and Donnie are playfully laughing and throwing popcorn at each other while half-watching Space Heroes: TNG with Raph. This is immediately followed by Raph encountering  Leo training with Karai. Raph later sees Mikey is chatting with Renet with "future tech." All of this is juxtaposition for Raphael being temporarily alone. If April were still romantically bouncing between Donnie and Casey, showing those Donnie and April together (especially with April instigating a lot of the goofing around, so it's not Donnie with hearts for eyes) wouldn't make much sense.

I doubt they will ever come out and make it more blatant, but all evidince leans towards Donnie/April being a "thing" and not just a joke. She already chose Donnie and vice versa.