Board Thread:Speculation House/@comment-25555436-20150721231017/@comment-26206856-20150726023858

I don't really see him cheating. Though after reading | this thread, I've deduced a new opinion about Raven. I see the two having Yang, and then they either have a fight or drift apart over moral ideals, and Raven leaves for a different lifestyle outside the kingdom and under the grimm mask.

With Raven gone, Summer kicks in either as the close friend who develops feelings after supporting Taiyang through the heartache of Raven leaving, or simply as a new love. They have Ruby, and the rest is history. Taiyang may not mention Raven since he doesn't want his daughters following her footsteps outside the safety of the kingdoms, or possibly following in a similar non-individualistic lifestyle. If Summer was close with Raven, she may have been killed following after her on a 'mission' (much like Yang is today) by grimm/the outsiders, or possibly even a jealous Raven like you mentioned. Again, the vagueness of this could be supported if Taiyang is trying to keep the facts about Raven away from his daughters.