Say ,,

Yup. Read Kashikomarimashita Destiny. :) The second couple, one is a beta and the other is alpha. http://www.mangago.me/read-manga/kashikomarimashita_destiny/

There's a yaoi, Kashikomarimashita, Destiny, where you can find your answer (;

Depends on the author/storyline I guess. Some have strict guidelines of alphaxomega pairing i.e. author wants it to be that way! But there are stories like kashikomarimashita destiny where we have alphaxbeta couples!

There is also a bete x alpha couple (not the main couple) there and they suffer a lot : http://www.mangago.me/read-manga/sayonara_koibito_mata_kite_tomodachi/

Yup definitely