Is saying, "I swear by God that if I don't do what I say, everything between us will end," considered an oath, and is it permissible to break it, and what is required of the one who says it if he is unable to abide by it?

What is apparent is that an oath is not established merely by writing without intention, and that writing an oath is considered a metonymy (kinayah). So, if an oath by Allah is written without intending it, it is not established. The evidence for this is that uttering the oath is a condition, and the Shafi’is hold that explicit writing is considered a metonymy, and an oath by Allah is not established by metonymy. Therefore, as long as the intention is absent when writing, no expiation is required upon violating it. In addition, it is not permissible for a man and a woman to establish a friendly relationship.