Helaena has "no taste" for riding...?
Not that I want to give the showrunners a good excuse for the shameless lack of Helaena+Dreamfyre scenes but....
When I first watched S2E08 and Alicent pushed back against Heleana flying Dreamfyre and said "And who will she be if her mind is broken?" ... I just assumed she was recognizing the trauma that flying Dreamfyre into battle would do to someone as sensitive as Helaena.
But now I'm wondering if it's a specific reference to past events. Perhaps Helaena attempted to ride her dragon and the (presumed) psychic bond between her and Dreamfyre was too overwhelming. Even Rhaenyra's comment that Helaena "has no taste" for riding sounds intentionally vague and unconvincing, as if it's a public cover story, or a polite euphemism for "Dreamfyre will psychically melt her brain."
Maybe that's why Helaena sticks with bug companions -- their brains are too primitive to psychically connect with her (or at least overwhelm her).
Possibly worth noting too that while Dreamfyre was never a war dragon, she was first ridden by Rhaena -- someone who went through a lot of terrible shit and fed her second husband to her dragon. So Dreamfyre might have some distressing memories. I wouldn't expect the show to go into that though.