What should someone do if he sucks at programming but still loves it?

Figure out why he sucks and try to improve. Maybe he just needs a different way to learn. Maybe the problems he's working on just aren't interesting or may be beyond his ability.

At least he probably has that passion to keep him motivated.
Imagine not being good at something, and also not liking it?

If he's really passionate to code and loves doing it. That means eventually he learns his way up and becomes better at it.

Everyone starts somewhere. Just giving him time and the support would bring him to places.

Study, practice, just hack your way until you feel confident about it. No one is born knowing, there is no such thing as talent. So at some time you'll just be as good

It's a journey, imagine yourself as a game character, you start out low and overtime you obviously progress and get better! Keep doing what you love, that's just it :)

Keep at it!

What do you mean by "sucks"?
Not as good as Linus, Richi or other top dev?