He'd rather die than marry her. She's his best friend's widow and a traitor to England.
She'd rather die than marry him. It's his fault that she is homeless, powerless, and might literally lose her head.
Now the king wants them married and living in Wales to help quell the rebellion there. Edward 1 is a very smart king, but a marriage based on betrayal and distrust can't possibly bring peace to a conquered territory. It's more likely to get them both killed.
Can these two enemies overcome stubborn hatred, and a nation full of problems to earn a lifetime of love, or will their mutual antipathy and unseen enemies cause their death?