Cattāri Brahmavihārā

This is specifically for romantic relationships but I suppose it could work for any relationship.

1. Recognize that kilesa (lust) formed the basis of your relationship. Recognize that both of you followed your enflamed desire in the pursuit of pleasure. Cultivate pañña and upsell ha, reflecting on the fact that unskillful actions always ripen in bad results.
2. Make the aditthana (determination) that all relationships you enter into be dedicated to the pursuit of virtue and will be based on the Dhamma. Allow any adhammic, akusala relationships to run their course. Do not add fuel to them through resistance, anger or jealous speech. Forbear. Cultivate khanti.
3. Clearly acknowledge their behavior as being unskillful. Contemplate how they must feel inside to be able to act this way. Contemplate on the fact that all beings are the owners of their kamma. Cultivate compassion for how they’re suffering now and how they are planting seeds of future suffering. Practice tonglen for them.
4. Reflect on the goodness they do exhibit. If you can’t do that at least be grateful for what blessings they have in their life. Recall that all beings have been our mothers and our children in past lives. Use this opening to cultivate mettā or karuna for them.
5. Dedicate merit to them on a daily basis. If possible, make a gift or offering of service to them and dedicate the merit of this gift to them.