Relationships why have them?

In the last post on negotiation I mentioned that I might answer this question in another post, here it is.

So why would people have relationships?

1. Love and/or Friendship: The desire to cultivate commonality in a personal and lasting way with a person you enjoy spending time with.
2. To meet some need: The meeting of a financial, emotional, sexual, spiritual, or intellectual need. This need meeting is not always inclusive of reason one.
3. Self Awareness: relationships are mirrors in which we see ourselves. Sometimes we can only see ourselves clearly by dealing with others. Granted this is pretty much a spiritual need but it was important enough to mention separately.
4. Raising children: Many people believe that in order to properly parent there must be two people. 
5. To appear socially acceptable: As if it is a duty to grow up, get married, and have kids to be a valid member of the "grown up club". I have a single friend who complains about people always trying to marry her off to someone in an effort to "help her feel complete". 
6. Control/self esteem: Abusive or not this one is pretty much a one way street.
7. Survival: I have seen this in relationships where the woman or man has a financial need and will pretend to be in love with/have sex with/and put up with abuse for financial support. 
8. Comfort or convenience: A person will sometimes allow someone else to be responsible for their comfort in exchange for some other form of support. (i.e. regular sex, a sense of belonging, not having to do their own laundry, a sense of security or stability etc.)
9. No man is an island: I had a person site this as a reason. They meant more that you can't help but have relationships with people unless you are a hermit. While in some ways this may appear to be true, I know people who are acquainted with many people but do not have active, mutually participative relationships. Modern technology makes hermit life even more likely. How long has it been since you picked up the phone and called or had coffee with a friend on Facebook? Is it still a relationship if you don't actively communicate?

OK. Many of these reasons relate to meeting some need. It's true humans do need to feel that they belong, survival is more likely in a group, and comfort and convenience are factors that encourage self awareness. So I have said what I think. What do you think? What are your reasons for having relationships?