Don't feel guilty in the slightest! I felt the same way, as my treatment course was relatively easy, comparatively speaking, in terms of side effects. That is simply the nature of the beast -- some are better, some are worse. My battle now is with the radiation fibrosis -- nothing dire, just annoying ;-)

Finishing treatment is a big deal. Just be prepared for some depression/edginess on his part over the coming weeks. I am still working through that, and am told it is common once treatment is over.

Congratulations on a big step!!