One can’t choose relationship without first choosing fidelity. Fidelity is the choice. Some aspects of fidelity and infidelity are natural. We is (or can be) transcendent of the so-called human condition. If two (or more) will it to be.
Why so-called? Because “human” applied to us is inexact. Humans are not static. Humans are in flux, evolving. Some are here; some there. Do not confuse a signifier for the signified. Language approximates; it is useful, but can mislead.
Am I free? Chosen will is a better term than free will. I can choose something even when I am seemingly forced to choose something else. This suggests possibility of a chosen will. Choice.