Zooey: Your husband, a Catholic, apparently married another Catholic in the church at age 17. Right? That marriage appears to be valid. However, due to his young age, there might be grounds for an annulment of that marriage.
Because any marriage of a Catholic to a Catholic in the church is considered valid, that first marriage of his is considered valid. So, when your husband divorced, the first thing he should have done (and still should do) is to consult the area Tribunal and petition for an annulment, at least on the grounds of immaturity (at age 17), and for any other grounds there might be.
If the annulment is granted on those grounds, then and ONLY then is he free to contract a second marriage. Since he is presumed validly married to the first wife, and since obviously you and he did not marry in the Church as he wasn’t free to marry you, your marriage is NOT valid (though it is civilly speaking legal and your children if any are legitimate) in the Church and you are thus living in mortal sin.
I know you are probably a very nice person, following your faith, but hon, you can’t just pick and choose what you’re going to believe and follow! You can’t be married validly to a divorced man unless his marriage has been annulled. It doesn’t matter that it has lasted 28 years–or 82 years for that matter. It doesn’t matter that you had a Catholic education or that you raise your children Catholic. The Church doesn’t change its rules around to suit people’s desires–people are the ones who need to conform their desires to the rules of the church.
It isn’t “the Church” that needs to change, it’s you and your husband. If he gets an annulment, then you can go ahead and get your marriage “convalidated” or whatever is necessary to make it not just a legal civil but a valid sacramental marriage. But it’s up to you and your husband to follow the rules, not for the church to change the rules.
Your religion didn’t “let you down”, zooey. . .you let IT down by knowingly and deliberately flouting the rules and then expecting them to change because you’ve “been married to him only for 28 whole years”.
You know what to do about this; I know you know it, you had a Catholic education and you felt it was right enough and important enough that you had your children educated too.