Ellie's romantic past with Cat should've been cut?

Ellie seems to have had a relatively long-term relationship with Cat. Ellie seems to have been startled initially when Cat took the initiative and kissed her, thinking that she might have infected her. She also tattooed Ellie's arm to cover her bite-mark (does she know Ellie is immune?). Dina even gets all jelly when talking about Cat, so we can assume it was at least semi-serious.

All of this seems to suggest that she had moved on from Riley's death pretty quickly, which is astonishing considering that Riley is the most significant source of Ellie's survivor guilt (let's be real here, ellie probably had to shoot riley when she turned - we know how much clem struggled with that for years). I can't help but wonder if this whole romance thing could've been cut.

Imagine if Ellie had loved Dina for 4 years but didn't act on it or divulge her feelings to her because she thought that if she got intimate with someone, she'd infect them. when Dina eventually makes a move, she's similarly startled, and her sense of apprehension at that moment would be a much better reason for her to flip the table on joel in front of everyone. Her visceral anger at Joel at the dance was still understandable, but it would've been even more so had that kiss been the first one that Ellie had since riley. Joel of course doesn't understand what's going on, and is incredibly hurt. A couple of days pass and nothing happens to Dina. She now realizes that she can have a normal, happy life. Why shouldn't Joel, someone she cares immensely about, have a chance to be part of it. So she decides to try and fix her broken relationship with Joel, and subsequently meets him on his porch.