What does it mean when he says I don’t deserve you?

We have been together almost 3 months. And he wants to go after a promotion. So I have been supporting him the whole time. He said “I really appreciate you being so supportive. I really don’t deserve you.” I know I hear when guys say that it’s a bad sign. So is it a bad sign?
What does it mean when he says I don’t deserve you?
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