Jimmy and Heloise's "R&B Soul Duet" in Misery Hearts is absolutely adorable and heartwarming. The fact Jimmy also spends majority of that episode trying to cheer Heloise up by finishing her story (even if he has no idea what he's doing) is also incredibly sweet.
Similar to the above, the ending of Fused Together with Jimmy and Heloise cuddling together as a heart made out of fire surrounds them, is likely to produce a few squees from the audience.
The ending of Heloise's Secret Admirer, where she rides a spin-dashing Jimmy, saying in a somewhat satisfied tone of "I'll take what I can get", is par for the progress she's making with him, before the two crash into her trap wall. Both looking beaten up, she says that she just wants to stay right there is another sweet touch as the episode ends with a heart.
From Bird Brained:
Jimmy: I mean, you'd come if I called, right? Heloise: Absolutely! (lovesick sigh)
Pretty much anytime Heloise shows off her softer side. It wouldn't be noticable except for the fact that...you know, it's Heloise.
"You know, Jimmy, I don't consider you an outsider."
Heloise and Beezy ditching the bribes Lucius offered and sticking by Jimmy in Jimmy on the Spot.