Does fasting become invalid by enjoying the reading of immoral and arousing words and descriptions, and is expiation obligatory for one who does that with the prior intention of doing what invalidates the fast and then atoning for it?

Fasting is not invalidated merely by reading something that incites desire unless it results in the emission of semen. The assumption that this invalidates the fast does not affect the legal ruling. However, if the reading leads to the emission of semen, the fast is invalidated. One must fear Allah and abstain from sins.