Our son is breaking up our marriage!?

Your wife has the problem really. Tell her, again, that you are not happy with this situation as it is not psychologically healthy for you OR your son.Tell her it is something that will force you to go to a counsellor about, and she will have to come too, in order to undo the harm she has done to your marriage. Who knows why she is doing this! Only a therapist could es her and find out the problem, which could stem from her insecurities. Goodluck.