If your date has an Ex, it is important to evaluate the relationship between them. After all, unless they were only married for a short time, there is still an emotional connection to that other person, for better or for worse.
If their relationship is civil but hating each others guts, then the Ex. only has a negative influence on your date. But, if the Ex is still best friends with your date, then the Ex is a force to be reconciled with.
Unfortunately, your date will never give you an honest answer about their relationship to their Ex. No one wants to present their Ex in a negative light. After all, saying negative things about their Ex only presents themselves in a negative light. Likewise, no one wants to seem giddy about their Ex. as that would imply that they are still in love.
Unless you can observe how the two of them interact face to face, the best that you can do is to pick up on subtle clues. Do they seem angry at the mention of their Exs name or do they smile? Do they mention any faults that their Ex has or do they only comment on the positive?
Assessing the Ex is vital to your relationship with you date because, like it or not, the Ex is a player in your relationship.