Years ago at a Dolly Parton concert in Sydney, Australia, the singer bragged about having such a long lasting marriage. She then said she is often asked the secret to the long lasting union. She said she always answers "I just stay gone." Everyone in the audience laughed, but does she have a point?
Oprah Winfrey used to also often say that the secret to her romance with Stedman was that they both had their own interests. Perhaps independence is key.
Spending every day together is a given at the start of a relationship - when two people cannot get enough of one another. After a while the reality of living together can become at best mundane at worst annoying. It is healthy to spend time apart. Being too co-dependent can drive anyone crazy. It is healthy to have other friends that you want to spend time with and it is interesting to talk with other people - get other perspectives.
Individual hobbies make life interesting. It gives you something to talk about with each other when you come back together. It also doesn't hurt for your partner to sometimes miss you. Independence is attractive. Think about before you got together - they were their own independent being. That is appealing.
Getting together with friends is key to a good relationship. Women need to talk to each other. You can't talk to your partner about your partner. You need to chat it out with buddies or family. This can give you another really healthy, objective, and outside view of your relationship. When you vent to your partner it can easily escalate into an argument because basically what they are hearing is you criticising and attacking them. Talking to a friend about it, gets it off your chest. Your friend can help you to laugh about it or seek solutions to more serious problems.
The bottom line is get away to stay together, if its good enough for Dolly and Oprah then its good enough for you.