I think Hana is "bullying" Yuki to protect her and their relationship.
Yuki seems to be a introvert and low in the hierarchy which makes her a easy target.
If Hana left her alone someone else would do it instead, not to mention the probable homophobia that would ruin their lives if they came out.
This way they can be as close as possible without anyone interfering and disguise affection as bullying.