 If you liked
Domestic na Kanojo
|
 ...then you might like
Unbalance x3
|
Both include a mature sister love relationship that are considered taboo.
MC is a student in both series.
Domestic na Kanojo is more of how the MC adapts to his new family/both sisters. Unbalance x3 (at least until now, chap 61) focuses on the brother-sister in love relationship.