Good points, cap. The only explanation I can think of aside from the one Navaros provided is that maybe the host itself (rather than the symbiont/slug) can actually choose to withhold certain feelings from its successors. This would explain why the ritual of communicating with past hosts is necessary at all. What's the point if the new host already knows everything the past hosts felt and did?
Torias may have been aware that his feelings for his wife could negatively affect future hosts, but maybe he never took that into consideration. And even if he did, it's possible he just didn't want to withhold them from his successors because he was too proud of those feelings to bury them. Maybe he just really loved his wife and didn't want to hide that, regardless of the possible consequences.
Also, it takes a lot of foresight to think, "I better not let my new host know about these feelings, just in case he or she comes into contact with my wife's new host someday".
I could easily see Torias overlooking that, especially since he's always been identified as the most nervous, awkward, clumsy, and reckless of Dax's hosts.