There is one exception called the Pauline Privilege. You can check out the
Catholic Encyclopedia article on the subject (scroll halfway down the page). It only applies to a person who, while validly married, is married to someone who is 1) not a validly baptized Christian and 2) harming the marriage by rejection of the Christian faith in various ways.
If your putative boyfriend was married to a non-Christian (we’re not talking merely non-Catholic) whose lack of faith or rejection of the faith, in part, destroyed their marriage, then that man is free to remarry.
Caveat: that’s the general idea, and I may be wrong in my specifics. Please check with a canon lawyer to make sure, both of the concept, and how the rule applies to him.
If that doesn’t work out, you would have to wait for an annulment or his wife’s death for it to be permissible to date. Technically, you could probably have a platonic friendship, but these are fraught with danger and are probably discouraged under most circumstances.
I will offer a prayer for the three of you. God bless!