Here y'go Ms. Sorcha:

May thou now rest in peace,
Knowing thou hast taken love from my heart.
Thou shalt not live in pain
For thou hast died.
Thou hast left all loved ones,
Now, thou hast been disowned.

'Thou' is nominative case, 2nd person pronoun form, used familiarly in the 17th century for the pronoun used as the subject of the verb;

'Thee' is accusative case for the same pronoun form, used when the pronoun is the object of the verb; that usage does not appear here;

'Thy' is genitive case, same person form, commonly known as 'possessive' case; that usage does not appear here.

Fine poem.

Merry Christmas

Bill Foster