"Forced"? There have been big hints throughout the season, starting with the fact that Ashi was the only one out of the septuplets that was given an actual name, indicating she's the one that would become an actual character and we'd see through the entirety of the season, so she'd have a bigger role than expected. Episode 3 foreshadowed it with the deers, and episode 4 is where it began development and in that same episode there was one major hint where the puff ball says "What did you expect, a hug and a kiss?", and that came from Jack's subconscious, so deep down he was kind of expecting it. Then there's Jack complementing Ashi's new look. It's the small details that I'm surprised not many noticed, but this is a case where it works. So it's not "just one episode", Genndy planned it from the start. Speaking of whom, this show is based off his dream where he's basically Jack and Ashi is his dream girlfriend. He doesn't do shows based on what people/YOU like, he makes them based on what he likes and this is what he always wanted.
Also, Jack’s been cock teased many times before, they’ve either turned on him or turned out to be a guy in disguise (Aku, seriously, low blow), and now he finally meets a girl that is just like him in every aspect and have a lot in common. Hell, they NEEDED each other to heal both physically and mentally, something they probably couldn't have done by himself, Ashi needed Jack to show her the truth about Aku and give her a new outlook on life, and Jack needed Ashi to break him away from his demons and remind him what a real hero he is and all the good he’s done so he can regain his will to live again. Jack's truth on Aku saved Ashi's life and Ashi's newfound hope saved Jack's life. Also, Ashi's upbringing hasn't been a happy one, all she's known was abuse and hatred from childhood to adulthood, Jack has been the only person in her life to show her kindness and understanding without any self interest and has been rather sweet with her, you think she'd pass that up?
They both have suffered enough, even legitimate badasses like them deserve some happiness too. As the old saying goes: “There’s always someone for everyone”.