Google Edward II. See also Henry Darnley. See Shakespeare's Sonnet 22. See the remarks made about Marlowe.
But keep in mind that the concept of homosexuality, of sexual orientation, are very modern. Elizabethans thought more of specific sex acts than sexual orientation.
This is an exceedingly important point.
The Celts as a set of peoples and cultures covers a giant range of eras (thousands of years) and several languages, some of which are not mutually understandable without deliberate effort.
We also know for a fact, both from iconography and...