How is Yahweh not immoral?

[Undeceived]

"I love those who love me

That's the root of the problem. Anyone loves people who love him. Even Adolf Hitler loved Eva Braun. The problem is not about whom you love or you don't love (you're free to love or not love anyone you want) but what you do to people you don't love.

Does it say "I love only those who love me"? Rather, the word for "love" attributed to God here is an active, giving love in response to our openness. 1 John 4:19 says, "We love because he first loved us." If you don't see the connection, take Romans 5:6-8:

You see, at just the right time, when we were still powerless, Christ died for the ungodly. Very rarely will anyone die for a righteous person, though for a good person someone might possibly dare to die. But God demonstrates his own love for us in this: While we were still sinners, Christ died for us.

By most accounts, the idea of loving your enemies originated from the Bible. That's what agape is--sacrificial love. In most religions there is a "golden rule"-

Confucianism: “Do not impose on others what you do not wish for yourself.”
Buddhism: "Hurt not others in ways that you yourself would find hurtful."
Hinduism: "One should never do that to another which one regards as injurious to one’s own self."
Humanism: "Do not do to others what you would not want them to do to you."
Jesus: "So in everything, do to others what you would have them do to you, for this sums up the Law and the Prophets."

Do you see the difference?

However, when I judge him as a character, I see that he is portrayed as a vengeful, petty psychopath, who on top of that is also a hypocrite.

Keep in mind that God is not human, and does not have the same motivations and emotions for his creation that a man would have for his equal. Do you see any reason why an all powerful creator would be vengeful? Do you see why an omniscient God would act without the moral code he instilled in his creation? What you propose is an illogical character. Even in analyzing fiction, the critic must always assume the author is keeping things consistent in order to understand the work (more so if the work is deep and hard to understand). If you followed the path of a novel critic, you would judge the book by its own principles. Do God's actions make sense given the Bible's description of him? Let's see, he is all-just and all-good. Nothing non-good can enter his presence. Any lives terminated had carried non-good and were unwilling to give the non-good up. God saw that no one could completely give non-good up, so he sent a sacrifice to take that non-good away from us. Like all gifts, we must consent or agree to it (lest free will becomes compulsion). Or here's an analogy: Martha's son Tim jumps in a mud puddle. Martha tells him, "You cannot come back in the house until you spray yourself off with that hose." Tim refuses. She walks outside and turns the hose on. The boy runs away across the street. In doing so, he is hit by a car and dies, because it was dark and the driver couldn't see him with all that mud on. Now who's the rational character in this story? If you say the mother, the Bible checks out just fine.

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It is not my fault that God could only choose to 'forgive' by submitting his 'son' to a horrifying death.

Of course it's not your fault. But death was the only way God could remove your sin from you. Jesus already did the deed, out of his own choice. All you have to do is accept it.