I have to agree with Leroy. As long as you're aware of the boundaries and have great communication with your S/O then it's ok. Once the relationship with someone else begins to make your S/O feel threatened in any way, you've crossed it.

I try to imagine that my wife can see me anywhere I am, and that keeps me out of trouble. I'm very lucky though that my wife is not at all the jealous type, and neither am I.

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"Old man, how is it that you can hear these things?

Young man, how is it that you do not?"