You say the sex isn't good any more.

Is it dull and repetitive, or is it just unsatisfying, or

is she making it difficult to enjoy the act?

The problems call for different apporaches.

Work out why you're unhappy with the relations,

what will fix it and talk with her.

If she won't talk initially, suggest a counseller.

Tough one.

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Calm, quiet, smooth, devastating