I am the same way. At work I've always been in sales or something involving dealing with people. Now I am a certified peer specialist helping others recover from mental illness. It is quite rewarding. Yet in the evening I am a hermit and don't go out much. In fact I had a relationship end a little while ago and having trouble with the alone part. I will get used to it but it's hard for a while.
I find I am like a loyal dog I do good in a relationship because I am not a go out kind of person either. My parents are the same way and I think it's not as uncommon as we think. Media is always making it appear that we're suppose to be social butterflies when I don't think that's the case for a lot of us.
I do know that things like Psych Central and Facebook help with the isolation. I am on the computer more when I am single trying to get that feeling of lonliness to subside.