Why can't I see no good qualities in myself?

You are your harshest critic. I've been there and I get how it feels to not see anything positive in yourself. No matter how untrue that may be. Something that can help is asking your friends/people you trust to name a couple things they like about you. That way, it can help you remember that you do in fact mean a lot to many people, and that you DO have good qualities, even if you can't see them yourself.