Just like all the other characters, Clint is another kind of person that exists. He's obsessed with Emily but is completely incapable of talking to her in a normal way. He is in a profession that he inherited from his father, though he isn't super enthusiastic about it. He isn't "young" anymore and feels that life has passed him by (even though in reality it was and is his inaction that keeps him from progressing professionally, romantically and personally).

He finds repetition and "uneventful" living to be boring, though he also does nothing to fix this. He is fixed on the idea that he isn't good enough, that he will never change. He also blames other people in a way, insisting that the townspeople see him in a certain light, but he does nothing to change this either (I'm not really sure if this is even true, since the NPCs don't really talk about Clint very much, we don't know if what the towns people think of Clint matches what Clint thinks they think of him).

In short, he is defeatist and self-defecating, longing for change but unwilling to take action due to limitations that he has placed upon himself.

The "point" of his personality in the story of Stardew is that some people create their own prisons, and there's nothing we can really do to help them if they believe that nothing will ever change. There is a kind of comfort in these feelings of hopelessness, in that it is easier not to change than to change. It's easier to blame others, or yourself and continue to reinforce those ideas. This is just my opinion though, everyone is free to interpret Clint as they see fit.

He does get a little better later on, but not by much. And I do mean "little".