Possibly he's tarnishing you with the same brush as your sister? Which isnt fair. Maybe, since your sister asked and got herself into debt that he's just a bit cautious.

It's so sad that he's gone about this in a negative way. But, maybe see it from his point of view about whats happened in the past with your sister and try to discuss this with him. (Even though its not right to tarnish you)

Im sure that this is not going to change things right now. But I'd be inclined to discuss it anyway. Just to see why he made this decision, otherwise your always gonna be wondering.

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I got muffins on the 30th September 2006