I can't relate for two reasons;
One, I didn't missed out.
Therefore, I know what it was like and appreciate it.
So yes, relationships do make me happy. And therefore there's no sour grapes -- yet I simply know it's too sweet for my tastes.
Two, I'm not even interested. Loneliness is a foreign concept to me.
In spite of the first part, I have no real social need nor had social drive. I can lose relationships one day and miss it all in reminisce and sentiment.
But I also don't see the need to fill the gap right after. Not out of bitterness and hurt, but simply from the lack of need.
When I'm with someone, either I have to get very tired and be happy with it... Or just be very tired, with all loss and no gain return on investment.
When I'm alone, either I get to be happy and satisfied... Or just be mad bored, which is the closest thing I got for a social drive.
But sure, I do have a lot of choices. 