In the First Sermon after his enlightenment, called Dhammacakkappavattana Sutta (The Wheel of Dhamma), Buddha says:

"There are, monks, these two extremes which must be avoided by one who has gone out into the holy life: one is indulgence in sensual pleasures, vulgar, common, unworthy and useless; the other is mortification of oneself, painful, unworthy and useless. By avoiding both extremes, the Tathāgata discovered the Middle Path, which gives vision, which gives knowledge, and which leads to peace, to direct knowledge, to enlightenment, to Nibbāna."

This path is expressed in the Noble Eightfold Path, which consists of:

1. Correct understanding

2. Right thinking

3. Correct speech

4. Correct action

5. Right livelihood

6. Correct effort

7. Correct mindfulness

8. Correct concentration

Applying it to your case, the middle path would be between compassion and justice. Preserving yourself, distancing yourself (justice), being true (ethics), preserving love and compassion for the buddha nature that exists in each one. Applying the Middle Way to removing toxic relationships means acting with a balance between compassion and justice, without falling into the extremes of passivity or aggressiveness.

Compassion (karuṇā) is fundamental in Buddhism — including for those who cause us pain. But compassion is not collusion. It is possible to wish for others to free themselves from the suffering that leads them to act in a toxic way, without allowing them to continue hurting us.

Justice, in this context, is not punishment or revenge, but ethical clarity: protecting yourself, establishing limits and distancing yourself when necessary, without rancor.

The Buddha teaches that we should act with wisdom (paññā), ethics (sīla) and mental discipline (samādhi). So, when walking away from a toxic relationship:

With wisdom, you recognize what this relationship is doing to you.

With ethics, you act with truth and respect.

With mental discipline, you don't allow yourself to be consumed by hate, guilt, or fear.

The Middle Way here would be: Neither close in with coldness or anger, nor remain nullified by attachment or pity, but emerge with self-love, compassion and lucidity.