Sentence (1) It was my fault for not making you laugh means that something was the speaker's fault and that the reason for that was not making the other person laugh.
Sentence (3) It was my fault not to make you laugh / It was my fault not making you laugh means that failing to make the other person laugh was the speaker's fault.
Let's imagine some context:
A. I believed his story. I thought he was speaking seriously. B. It was my fault for not making you laugh (The fact that you believed his story was my fault. If I had made you laugh, you would have realized he was pulling your leg).
A. I cried a lot. B. It was my fault not making you laugh (I should have made you laugh, not cry).
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