Though indifference is the opposite of love, it is not negative in all circumstances. Indifference is a response that is completely detached and therefore without emotional energy; it relies on rational feelings instead. Like most things in life, indifference needs balancing. Indifference is beneficial when considering the affair relationship. MLCers affair down; let that be a reassurance rather than a frustration. Acceptance of the reality of the affair relationship will enable you to detach from it more easily; you will be indifferent to their relationship because you know the eventual outcome.
Indifference can be a beneficial step toward detachment which is a necessary and healthy part of Standing and Paving the Way. But there is also a danger that with indifference you will go beyond healthy detachment from your MLCer's emotions and cycling behaviors and will additionally detach from your own feelings and emotions toward your MLCer. This is when you will feel you no longer love him or care what happens to him. But this level of indifference may not be complete indifference in that it may circle back to an attachment through demonization and hatred. I'm not saying that not caring about what happens to your MLCer is bad, but it is not beneficial to Standing. For those who do not want to restore their marriage, perhaps it is a necessary step for the process of moving forward without your marriage and possibly opening yourself to new relationships in the future.
Indifference can help you to move through your emotions such as anger and learn to respond instead of react. Your anger is important, it shows you care, but it is also reactive. If you are clinging to it rather than releasing it, you need help with release. Indifference is non-reactive. You may interpret some of your MLCer's behaviors as indifferent. But if their behaviors are motivated to incite a reaction from you, they are indicative of attachment; indifference does not attempt to incite reactions.
Your MLCer may mask depression with what seems like indifference--or you may interpret depression as indifference. Being depressed feels like you are without a soul, a foundation, a way out and are stuck in the Wasteland. It feels permanent and thus hopeless. In Replay you may recognize the soul-void when you notice their eyes seem dead and they seem to act without a conscience. In Liminality depression becomes more overt and their entire demeanor is like the walking dead. They may seem restless because they want to stop moving and are immobile, unable or unwilling to drag themselves out of bed. Replayers may avoid eye contact, but as they become more proficient at deception, eye contact may resume. In Liminality they avoid eye contact not because they are lying and trying to avoid detection but because they want to disappear; they are trying to melt into the background. Depression may manifest as indifference or someone may interpret it as such. In a state of depression Self love lies buried beneath rubble and until it surfaces the MLCer is incapable of showing love for anything or anyone. There is no caring substance, understanding this can help you to avoid interpreting the lack of caring making it personal. It is not personal; he is dead inside.