4- In a marriage, do you think there are unforgivable things?

Adultery is for sure something that would be very difficult to forgive. However, it isn't impossible. Counseling would surely be helpful. Both have to be willing, but forgiveness is possible.

Here is an example, from a couple we know:  The couple had been married for several years but unfortunately the wife had an adulterous relationship with another man.  Eventually the truth came out and this seemingly beautiful marriage appeared ruined forever.  Both were Christians and did not want or believe in divorce but how could adultery be forgiven?  They had 5 children and the husband wanted to either “leave her or kill her.”  She was VERY sorry for what she had done and didn’t think she could ever be forgiven. She was sure she was doomed to go to hell. They confided the situation to good friends who emphasized the fact that Christ was part of their marriage since they had received the Sacrament. They went to a chapel where the Blessed Sacrament was exposed. There the husband accepted to forgive his wife. Because he released her from her guilt, she was able to make a real conversion. God always draws good out of evil. Both went to marriage counseling to continue to heal. They learned that adultery usually stems from deep-seated issues that Satan preys on to create problems in a marriage. For this couple, they both discovered some issues. The wife's were feelings of inadequacy. From a young age she never felt good enough and ended up seeking approval outside her marriage.  They both wanted to reconcile and were able to.  They still struggle with trust, Satan continually attacks but now they turn to the Lord. They will both tell you that although they would not wish this on anyone. Satan tried to destroy their marriage but God was able to make it even better.

Yet there are some situations in which living together becomes practically impossible for a variety of reasons. In such cases the Church permits the physical separation of the couple and their living apart. The spouses do not cease to be husband and wife before God and so are not free to contract a new union. In this difficult situation, the best solution would be, if possible, reconciliation. The Christian community is called to help these persons live out their situation in a Christian manner and in fidelity to their marriage bond which remains indissoluble. CCC 1649

Forgiveness doesn't only depend on our good will. Sometimes we have the desire to forgive but just can't. I always think of Christine's Mother's example: her father-in-law didn't like her and kept telling lies about her to Christine's Dad... After her Father-In-Law died, she wanted to forgive him but just couldn't. So she decided to ask the grace to forgive him to the Lord, every day... It took several years but one day, finally, the weight was gone, she could feel deep inside her that she had forgiven! Forgiveness sometimes doesn't happen overnight!

We are lucky that when God forgives, He also forgets! St. Thomas Aquinas, a doctor of the Church says that when we are forgiven through the Sacrament of Reconciliation, for God it is as if our sins never existed!