That is so sad. So many folks have that idea. Even if they have remarried outside the Church, they can STILL attend Mass, they just can't partake of Holy Communion. They can still be there to listen to God's Word and be with other believers.
I met a woman back in the 80's, who was part of my 'Renew' group, who attended Mass every Sunday, but was just in agony, because she thought she couldn't receive Communion. That is what the priest had told her when her husband divorced her about 20 years before. She had no inkling of the divorce until her husband's father told her it had happened. She was told by the priest that because she was divorced, she couldn't receive Communion anymore. That made her angry, because she had not asked for the divorce; it had been done without her knowledge. When we asked her if she had ever remarried, she said no. We told her that the priest had told her wrong, that there was no impediment to HER receiving Communion. She was reluctant to call the Pastor, so I told her I'd do it for her and find out what he had to say. When I told her the following week that our Pastor told her to come in to talk to him so she could go to Confession and be ready for Communion, she just burst into tears. The next weekend, I saw her in the line going up for Communion, and the look on her face was sheer joy!
**When we asked her if she had ever remarried, she said no.**
Thus, she could continue to receive Communion. Indeed, the priest was wrong.