Why do we stay when we know we should go?

I've been thinking about relationships lately. Nothing really specific or focused. Sometimes I think about what it is I want in one and if I'll ever be happy in a relationship again. And if there is a man out there for me, will I find him sooner rather than later?

I've also wondered why we stay in relationships that we know aren't good for us and make us unhappy. I think it's fair to say that just about all my friends are coupled off. While I think most of them are happy, I have 2 friends who clearly are not.

Despite attempts on their part to communicate with their partners in an effort to make things better, things are not better. One is married and seeing a therapist on her own and the other is living with her boyfriend in the suburbs. Both know deep down that they should leave, but they're scared to - the former because she doesn't want to be a 32 year old divorcee, and the latter because she's turning 34 this year and doesn't want to be 34 and single.

I admit that I wish I had a man in my life to share my interests with. While I have great friends and we are close, I miss being part of a couple and the simple intimacy of holding hands. So I guess the nagging question for me of late is whether it's better to be coupled off and unhappy, or single and relatively content?