Despite promising one another everlasting love

[Bassim]

Have I made any mistakes? I'm not sure if "ran away from her like a believer from the devil" is correct.

Despite promising one another everlasting love, Ruth and Paul soon understood that they were not right for each other. He had never set much store by material things and money, while she was a big spender. Her appetite for luxuries seemed to be insatiable, and he watched with alarm as their house was filling with all kinds of expensive articles they didn't need. Paul's love for Ruth was still strong and he believed she was going to restrain herself when she understood the folly of her compulsory buying. But when he discovered that she was borrowing money from a bank without paying it back, that was the last straw. He ran away from her like a believer from the devil.

 

[abaka]

Despite their vows of everlasting love, Ruth and Paul soon understood that they were not right for each other. He had never set much store by material things and money, while she was a big spender. Her appetite for luxuries seemed insatiable, and he watched with alarm as their house filled with all kinds of unnecessary expensive articles. Paul's love for Ruth was still strong and he believed she would restrain herself as she came to understand the folly of her compulsive buying. But when he discovered that she was borrowing money from a bank and not paying it back, that was the last straw. He ran away from her like a believer from the devil.

Vows -- they actually tried to stick together. One another should be "each other", but I struck it out to avoid repetition.
As she came to understand -- expresses Paul's hope for Ruth's eventual, unfulfilled conversion.
And not -- improves parallelism.
The last simile seems almost too strongly put, but I trust you meant it that way.