Hmmm......one moment of true happiness??? Well, just being a parent doesn't necessarily mean true happiness - I have 4 kids, and I love them all deeply, but I can't say that having them gave me a moment of true happiness - I felt overwhelmed and in awe, and loved them all before they were even in this world.
I also think the moment of true happiness that would mean Angel losing his soul, would happen when he was intimate with his soul mate so to speak - maybe Buffy was the only person he would ever know true happiness with?? He could sleep with other women, and yes, derive pleasure from it, but he wouldn't necessarily have that *moment* again.
I think the feelings he will experience for his son, are entirely different, you can love someone completely and still not be happy, in my opinion.🙂🙂
Just my feelings on it anyways.😉