Nor jealousy Was understood, the injur'd lover's hell.

Jealousy is the injured lover's hell

What frenzy dictates, jealousy believes

They play well together because there is no jealousy within the relationship, none whatsoever. The key is that there is no envy with the two of them.

Jealousy is being called up to what you can have, instead of called out for what you don't have.

Jealousy, that diseased crow pecking at your heart.