Ben doesn't love himself because he knows he's a total fraud. Phyllis knows it, too.
But Sally doesn't. So Ben, for a short period, gets to "return" to a time in his past when he was still able to fool Sally, Phyllis and...himself. The reunion offers him a moratorium on his self-loathing because he gets to spend time with a woman who was too naive to accept that the man she believed she was "in love" with was a first-class cad. I mean, even though he dumped her for Phyllis, Sally still carries a torch for him. Ben experiences a sort of redemption (albeit a rather brief one)...until "reality" rears its ugly head and he remembers that who he is today is only a more evolved and sophisticated version of himself from 20 years ago. The road he DID take never veered off the path to superficiality and deceit he started on when he was a young man.
You can lie to people and convince them that the reality you are creating for them is the one and only truth. But you always know it's a lie. And until you start living your life honestly, you will always be miserable. This is what, I believe, Ben begins to understand by show's end.
"Be on your guard! Jerks on the loose!"
http://www.roches.com/television/ss83kod.html
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"If any relationship involves a flow chart, get out of it...FAST!"
~ Best12Bars