Jonas has a unique relationship with The Giver. Whereas Jonas's other relationships are very constricted by societal norms, Jonas's relationship with The Giver is very open and stems from the assumption that Jonas and The Giver are the only two people in the community with actual feelings.
Ordinary relationships are very planned out in this society, not based on love. Jonas and The Giver have a relationship that is comparable to a father-son relationship and is based on love and mutual respect. The Giver teaches Jonas about love by telling him stories about his own experiences. He also teaches Jonas about fear and hunger. These very basic emotions resonate with Jonas and create a bond between him and The Giver that is dangerous, because that bond has the power to destroy Jonas emotionally. Emotions are not tolerated in this society, so that power reigns supreme in Jonas's life.
The Giver teaches Jonas more than just how to love. The Giver teaches Jonas to feel in a world where he is surrounded by unfeeling people. As in any society, "differentness" is dangerous. It is much safer to run with the herd, so to speak, and yet Jonas's relationship with The Giver has made him forever different. The danger in their relationship comes from The Giver's ability to teach Jonas how to feel. The fact that Jonas is now able to experience real emotion sets him apart from others in his community, and the danger lies in Jonas now being unique in a society of sameness.