Where do you draw the line between devotion and obsession?

Where do you draw the line between devotion and obsession?
I mean, I get told I'm lucky she's very loyal to me, but I like to joke it's obsession on her part and up to a point it actually is. It's always a thin line that separates loyalty and mental illness.
What about you?
Where do you draw the line between loyalty and obsession?
Where do you draw the line between devotion and obsession?
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