User blog comment:TheSt0ryTeller/Assassinews 09/26 - New AC3 Info and Videos!/@comment-121.127.202.151-20121011045228/@comment-3168501-20121011065219

They wanted to further the plot; if he settled with Rosa, then Revelations wouldn't have come out. And she's only a year younger than him, so if he was, say 50, when they settled down, she couldn't have kids or it'd be difficult. Plus, I think they had to scramble and do something quick because her voice actress died, so they basically wrote Rosa out of the story. I think they would have made her his main love interest if she were still alive. But they could have just gotten another voice actress...Oh well. I forgot her name, but the way she died was so tragic and unknown to us...