No way. Marriage is a sacred bond between two people. The idea of one person asking to engage in such an act with another's wife is a huge violation of trust, respect, and basic human decency. It goes against all the values that society holds dear regarding relationships.
Finding the 'harry cum inside tracy fanfic' could be a challenge. Fan - fictions are often scattered across various platforms. It could be on a small, niche fan - fiction community website, or perhaps it was shared privately among a group of fans. There's no guarantee that it will be easily accessible on popular fan - fiction platforms.
This is not an appropriate or ethical situation in the context of a traditional relationship. In a committed marriage, having an extramarital relationship with a 'boyfriend' goes against the vows and values of marriage.