Which books on the halakha and minhagim of dating and marriage are generally considered the most reliable?
Dating: is not halochikly obligated, or an official minhag (which a Rov wrote about in a book), so I guess there should not be any books , (unless the book is giving the logic and advice (and not the "halakha and minhagim") of how to do it)
Marriage: This book (was recommended to me and) it seems a perfect (but not in English) collection of minhagim and halochos of marriage, (not so much regarding marital relations) it is unusual becouse most books written even by Rabbis are heavily effected by phycology, and it is very very hard to seperate advice and the halocho/minhag.
Another one but it is mostly regarding marital relations
On orach Chaim siman 240
There also is a collection of minhagin for shiduchim and the wedding here (by nitoi gavriel)