He, Rose, and Ruby's biological father, Behr were all in the same social circle in their youth. The two young men had an... animosity for each other, to put it lightly. With Behr knowing of Eric's feelings for Rose, and yet he pursued her anyway, when Eric refused to take the leap. There was a noticeable divide between Rose and Eric afterwards, with them splitting up, until after both Ruby and Vil had been born, and both their spouses having died.
Eric saw this as a second chance, an opportunity to finally live the life with the woman he loved through his younger years... But Rose grew sick. She would never recover. and Eric would never be able to look at Ruby without seeing her father, afterwards. in his eyes, a cruel reminder of his own cowardliness
And instead of being a normal adult and seeking help, he would bully her. pick apart her appearance. her dark hair, her moles, her soft face- All things that not only made her look more like her father, but also more and more like Neige LeBlanche as she grew older. He wants to protect his son for more competition, he's grieving his lost love...
He will, eventually, come to regret it. He will eventually seek to make his family whole, but not without... Outside influence.
(This took so long to actually formulate a response hehe, hope it was worth it! I am still answering things in my inbox, dw <3)