The term self-preservation means doing what is best for your well being in everything you do; like hydrating or having a clean diet. It also means being able to know what energies you attract. In this case, one may not know at first, but the process of self-discovery teaches one a lot about the things that work for them and the things that don’t work.
Take for example the friends you had in high school, you may have thought you would stick with them for years to come but only to drift apart because your goals have changed, or you have found a different click. This does not mean they were bad; it just means they were good enough then when you were in that situation but now, they aren’t so aligned with your perspective.
This also includes the friends you kept for many years; they too have the one thing that no one else has. They possess the qualities that you depend on continuously even as you grow older. You know this because even when you hardly talk to them or see them you still feel the same energy when you are around them. It is however different for intimate relationships. Those teach you about tapping into your feelings and making sacrifices to be around a certain person. Bear in mind this person was but a stranger to you once and now they stand to be the best or worst thing in your life. Regardless of whether it lasts or not the chemistry you share has a way of being a constant reminder of what you have; for some even long after they have parted ways.
Essentially the bonds made tend to be the ones that stay behind and make one not stop caring about a certain individual. Notice how abusive relationships also have a stem and end up lasting for a very long time even though the connection seems tainted. A relationship between an abuser and the abused has a bond that external factors cannot combat.