There is no such thing.
I say this mainly in the context of situations going downhill that you have partial to no control over. Ones that are partly to completely your fault. Ones that you want to fix, but every attempt leads further down the path of separation.
You can never go so far, you can never screw up so much, you can never hurt someone enough to render the situation completely nonredeemable. Oh sure, you say. I know that.
Have you prayed for love, wisdom, and hope in this situation? Have you prayed that God would redeem it all? Have you been praying for someone, and then your relationship with them starts to disintegrate?
Don't give up. Pray for brokenness, humility, love, wisdom... and keep going. We often give up on these situations and people and seek to avoid them, we seek to withdraw our efforts when things get bad, when it hurts to face it.
Pray, and face it. It will be the most liberating thing you can do, having your Father break the fear out of you and stepping out in faith and courage to witness, to mend, and to rebuild.
If it gets worse, just remember: the situation is never beyond redemption. It can never be so far gone that God can't repair it. There is no such thing as the point of no return.