People don’t tend to be “good” or “bad” but usually just have various strengths and weaknesses. It sounds like this guy has an intense need for external validation, and your friend has an intense need for emotional attachment. As long as they stay as just friends and don’t become codependent, that should work out just fine; he’s probably right that as a romantic relationship there’s pretty much no way this one will work.
And that’s ignoring the “do either of them have abusive or manipulative tendencies” angle. The big thing is that neither of them should depend solely on the other for emotional fulfillment.