I think if you cant be happy with yourself, you are going to have a hard time being happy with anyone else.
Romance is fine, but in the end, friendship with your spouse / partner is more important.
One of the things I have learned from being married is that what you lack the other can bring to the partnership. My wife tends to be very serious and even dour, and I am stupid silly and like to laugh, and make her laugh. I suck at banking and paying bills, so she does that. I cook 100% of the time, she burns water. I tend to be much better at housekeeping, and she is better at other things. Oddly, our traditional gender rolls are reversed a lot of the time, but it works fine for us.
Marriage / romantic relationships really are give and take, and if you give far more than you take, or visa versa, there is something wrong with the blance of the relationship.
As others have said, seperate lives and interests are a good thing. If you are entwined 100% in the other, you loose a big part of yourself. I had a buddy who's wife was slowly eliminating the things he loved from his life, and I could see that it was not going to end well.
I guess in the end, those who are happy alone, for a few hours or a lifetime, are far stronger and happier overall. Alone doesnt have to mean lonely.
Dane