One ovelooked aspect of #fe3h, I think, is Rhea being a mother-figure to Byleth and the latter just...not being into it.

Rhea: You're like family to me, Byleth.
Byleth: Why.

Rhea: I've come to think of you as my ward.
Byleth: I'm 25. So. No.

Rhea: You've grown so much
Byleth: I don't know you.