I don't think in your case it would be a lie to say "It's not a good fit." Design is a pretty subjective area so it's likely the case someone else will find his work to be higher quality than you do. Maybe he's asking you for critiques because he can tell you aren't digging what he's producing, or maybe the vibe between you is no good and you're perceiving that as mediocre work. In any event, best to get it over with; you'll both be better off without one another it seems.
He's been with us for long enough we (meaning I) should have recognized that earlier, so part of the problem was my fault - poor management.
This just really sucks. It's like if I do poorly other people lose.
Maybe I'm overly sensitive to this because I've been fired before and it really sucked, but it was devastating. I don't want him to have the same experience I did, because he doesn't deserve it.
If you feel like taking the responsibility, financially, then give him a fair severance such that he can look for something new without ruining his situation.
