Does committing major sins or having perverted fantasies during masturbation, such as imagining wife-swapping, lead to the annulment of the marriage contract, and does sincere repentance from these fantasies remove their effect?

The husband's commission of major sins, such as "masturbation and fantasies," does not annul the marriage as long as he is a Muslim. However, practicing this habit is forbidden, and its prohibition is more severe for a married person. The husband must repent from it by abandoning it, regretting it, and resolving not to return to it. He must also beware of being negligent concerning obsessive thoughts. Among the things that will help him get rid of it are seeking Allah's help and frequent supplication.