No one would ‘risk his neck’ or gamble his reputation to vouch for or support the statement of an individual who has lied (to him or to others). In matrimonial relations, such scenario carries suspicion of infidelity; why would one lie to his/her spouse unless s/he has something to hide? Notwithstanding extenuating circumstances, the basis of such relation is trust.
If you can no longer trust your partner (spouse, fiancé (e), etc.) the relationship is undoubtedly on very rocky grounds. Any slight ‘turbulence’ at all can bring the house down, so to speak.
In the world of the MeToo movement however, this basic principle is thrown out of the window. Activists of the movement offer every possible scenario to explain away an individual evolving story about a possible sexual harassment or sexual assault (more on that later).