When the Relationship Fails
Long term relationships are a comfortable place for many people. They get used to their partner, and it takes less energy to compromise than beak up and move on in life. There have been a great many people that went to their graves unhappily married and full of regrets because of this attitude. These people found it easier to continually give in and ended up with nothing. While it is extremely difficult, sometimes life requires summoning the energy to make a major change. Leaving a long term relationship that has failed is sometimes one of them.
Having a long term partner means a person has someone they have come to know intimately. This is not just physical intimacy, but they know almost everything about their partner. For many people in long term relationships, there has been a great shock when their partner suddenly says they no longer want to be together. This often happens because inertia has built up in the relationship and there is no hope that anything will ever change.
For a person that has gone through this type of experience, the thought of dating again may be painful. Their trust has been broken by their long time partner. They believe they cannot summon enough energy to find someone else to date. Their best chance to get their life together may be finding out about fuck buddies. They need to learn that a fuck buddy is a safe bet for physical intimacy. This person doesn't want a relationship, so dating is not necessary.
For many people coming out of a long term relationship, casual sex helps them adjust to the world of dating. They have a safe partner with no expectations of a future relationship. This will serve them well as they learn how to meet and get to know new people.