Son compartido

Is this normal in a marriage, or am I making it into something. I’m trying to understand whether what I’m experiencing is actually normal in a marriage, because my husband insists that it is. We’ve been married for 13 years. This started around 5 years into our marriage, when our baby was about 1 year old. He began introducing fantasies involving other men into our intimacy. The first time it happened, I gave in to his fantasy. but felt extremely guilty the next day. I told him I wasn’t comfo