Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
It is forbidden for Muslims to read something which glorifies and glamorizes sins because this has a major effect on the mind.
Answering your question, Sheikh Mustafa Umar, President of California Islamic University, states:
It is forbidden for Muslims to read something which glorifies and glamorizes sins because this has a major effect on the mind.
Imagine reading a book about a person who loves to drink wine. The more details the book has, the more the reader is influenced mentally to want to do the same. This is well known in the field of psychology.
If there was a more scientific book which simply explained what was happening but did not glamorize it, then it would be allowed, but that is not what romance books do.
For more, see these fatwas:
Homosexuality and Lesbianism: Sexual Perversions?
Almighty Allah knows best.