Reading and Writing for the obsessed! discussion

I've been translating an opera that's never been translated into English before, and there's a part where one of the characters is referencing Greek or Roman mythology. I don't know what the myth is, or if it even exists, but if someone could help me find out, that'd be awesome!!

It's about 'Tiri' ('Tirsis') and 'Dorilla', a couple that is in love, but then Dorilla becomes unfaithful.

Here's the text of the aria...

Customs, wit, love,
These joined two pastors
And from two hearts
One was formed.
Merry were the spouses
As long as love lasted!
But in her, slowly,
The flame began to weaken.
It burned for another object,
That inconstant woman,
And that ill-bread affection
Caused suspicion in the husband.
And so he waited
For the faithless woman
And was one day surprised
In a way that I won’t say.
Shame, spite, and anger
Came from his lips.
So he created a wound
In both of their lives
And made their bodies bloody
Because of his unfaithful lover.
And on the dying lips
Of that unfaithful wife,
Her dying soul
Opened the doors,
And died a double death
Of a sword and of a broken heart.
Think, like in my unhappy Lilla,
A Tirsis and Dorilla
Are still able to be found.

Thank you in advance!!!

Ugh I know it i just can't think of it.

Well that's getting somewhere! I didn't recognize it.