My ex-husband's wife adopted my son. Can I get that reversed? My son is now 14.

It's possible, but it's likely to be difficult, if the adoption has been made final.  For that to have happened, the court would have had to terminate your parental rights.  This would have to have been based on a finding that you had not been enough of a mother to your son, for whatever reasons.

The only really strong chance you might have, is if you never got notice of the adoption proceedings until after they were over.  If that's the case, and you just found out about this, you must act immediately.  If you can prove that your right to notice wasn't honored, you could have the case re-opened, but only if you make your application to the court very quickly.