Koi Kaze, Kodomo no Jikan (TV) Recommendations
Both have an extreme theme about their respective romances. Both have a romance that is socially and morally unacceptable.
Jikan has a more humorous take on it. Koi Kaze is more serious and emotional.
Both of these anime explore the psychology and struggles of people with romantic feelings that are socially unacceptable. These definitely deal with controversial subjects, so these aren't for everyone, but if these forbidden relationships interest you, these are pretty good anime to explore them.