As Harrison said, the lyrics are not entirely coherent. I would read
that passage, a bit loosely, as "When I was happy (good times), I never
seemed to be as happy as [I could be][I am now]. I believed that I
might never be happier than I was then." The song continues
"But now (in contrast with "then") I look at the night and it don't
[sic] seem so lonely ...". He is happier than he was before.
I left two choices in brackets above because I think "so" there can be
interpreted as "very" or "by comparison with the present", and I can't
tell which he means.