What do you think about "assumed consent" in relationships?

This is a follow on from another thread. In particular, if I grab a random woman and kiss her, it is (and should be) assault. But if I grab my wife and kiss her, most (including her) would view it as a romantic gesture. But we've never explicitly discussed what is and isn't OK - it just seemed obvious.

How do you work out these issues of consent in a relationship? Does it work?

To be clear, I in no way suggesting any actions where the other person is clearly non-consenting, this is about cases where consent can be assumed if they say nothing.

What do you think about "assumed consent" in relationships?
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