That's assuming we don't colonize other planets, or meet other races. While the earth may turn into space dust, that doesn't mean you can't find somewhere else to live, or won't have SOME sort of technology to move you along. I'm sure, at some point within that theoretical 100 billion years, mankind would eventually get off this lump of dirt.
As for pain: A friend and I have had a deep discussion about this. Pain is a natural reaction to things that cause bodily harm and/or death. Just as fear is a reaction to the same. If you were completely, 100% immortal, could not die, could not be torn apart, rent asunder, shattered, obliterated, or so much as scratched, would your body even understand the concept of pain? Of fear? If you were born immortal, or if you suddenly became immortal, would it make a difference? Believe it or not, we've spent quite a few hours talking about this subject lol.
As for the question: I would, without a doubt, LOVE to live forever. My curiosity for what happens to humanity after I'm gone burns so intensely it's not even funny. I've actually gotten to the point where I HOPE there's some sort of after-life, so I can watch what becomes of our species.
As for loved ones/friends: After so many millenia, (wow, the spellcheck says that's misspelled...) you'd eventually become accustomed to that loss. Or, you'd just learn to live without. Personally, I'd feel so far removed from the human race that I wouldn't feel the need for a mate or even friends. My sole purpose in 'life' would be to stand by and watch what happens to us. I'm sure at some points in time I'd find myself bored and would take on a mate, or maybe some friends or something, but I can't imagine their loss would affect me much. Their lifespans would be so minuscule compared to mine, I'd barely miss them. Also, would the feeling of losing a loved one/friend fall under the category of pain? If you can't feel pain, and losing someone is considered pain, than you couldn't feel the pain of loss, could you?