If you mean aloneness, then i really don't know is the honest answer.
But in relation to the happiness bit, or as i prefer, the contentment by absence of suffering, i find periods of being alone deeply satisfying. I love getting up on days when there's nothing i have to do, no-one i have to meet, nothing on the agenda. Just see what happens, just see who i come across and so on.
I think the beginning of the answer lies with my frequent island visits (in south thailand) throughout the 90s, mostly for two or three weeks, and nearly always on my tod. Obviously i'd meet other people and enjoy their travel tales and so on, but it all happened kind of spontaneously, and only when i felt like talking.
Also, throughout my life i have observed so many petty arguments between couples, so much dependency shall we say, that it became clear to me that the biggest threat to our inner harmony is relationships, and i include family ones and friends.
I place freedom as the highest altar to achieve in life, followed by giving out love. I think when you get one, the other falls into place.
But if one is not content within, i can't see how you can give out love as a default for one's life. Hence the 'selfishness' that gmarthews mentioned just above. In reality through selfishness we can attain selflessness!