‘Tis hard to end a years-long love to-day;
‘Tis hard, achieve it then as best you may;
This victory win, this only safety trust,
Say not you cannot or you can — you must .
 
[Difficile est longum subito deponere amorem;
Difficile est, verum hoc qua libet efficias.
Una salus haec est, hoc est tibi pervincendum;
Hoc facias, sive id non pote sive pote.]

Catullus (c. 84 BC – c. 54 BC) Latin poet [Gaius Valerius Catullus]

Carmina # 76, ll. 17-20 [tr. MacNaghten (1925)]
    (Source)

On the need to break up with unfaithful Lesbia, his longtime love.

(Source (Latin)). Alternate translations:

At once to quench an ancient flame, I own,
Is truly hard; but still no efforts spare;
On this thy peace depends, on this alone;
Then possible, or not, o conquer there!
[tr. Nott (1795), # 73 "To Himself"]

'Tis hard to lay long-cherish'd love aside;
'Tis hard at once. But 'tis your only plan;
'Tis all your hope. This love must be defied;
Nor think you cannot, but assert you can.
[tr. Lamb (1821), "The Lover's Petition (To Himself)"]

'Tis hard at once to fling a love away,
That has been cherish'd with the faith of years.
'Tis hard -- but 'tis thy duty. Come what may,
Crush every record of its joys, its fears!
[tr. T. Martin (1861), "Remorse"]

'Tis hard to quench at once a long-nursed love;
'Tis hard -- but do it howsoe'er you may;
It is your only chance -- our courage prove --
Easy or difficult -- you must obey.
[tr. Cranstoun (1867), "To Himself. The Lover's Petition", st. 4]

What? it is hard long love so lightly to leave in a moment?
Hard; yet abides this one duty, to do it: obey.
Here lies safety alone, one victory must not fail thee.
One last stake to be lost haply, perhaps to be won.
[tr. Ellis (1871)]

Difficult 'tis indeed long Love to depose of a sudden,
Difficult 'tis, yet do e'en as thou deem to be best.
This be thy safe-guard sole; this conquest needs to be conquered;
This thou must do, thus act, whether thou cannot or can.
[tr. Burton (1893), "In Self-Gratulation"]

It is difficult suddenly to set aside a love of long standing; it is difficult, this is true, no matter how you do it. This is your one salvation, this you must fight to the finish; you must do it, whether it is possible or impossible.
[tr. Smithers (1894)]

'Tis hard to lay aside at will
The love of years, -- and yet, I trow,
What men erewhile have borne may still;
Be borne, though hard, and shall be now.
Borne, ay, and done -- done, whatsoe'er
The pain of doing. Here for me,
Lies the sole refuge from despair,
And the end of all this misery.
[tr. Harman (1897), "The Soliloquy of Catullus"]

It is difficult suddenly to lay aside a long-standing love. It is difficult; but you should accomplish it, one way or another. This is the only safety, this you must carry through, this you are to do, whether it is possible or impossible.
[tr. Warre Cornish (1904)]

It is not easy, at a moment's notice, to lay aside a life-long love. It is not easy; but yo must do so, what way you can: this is our one salvation and must be attained by you: possible or impossible, do it you must.
[tr. Stuttaford (1912)]

It is difficult suddenly to lay aside a long-cherished love. It is difficult; but you should accomplish it, one way or another. This is the only safety, this you must carry through, this you are to do, whether it is possible or impossible.
[tr. Warre Cornish (Loeb) (1913)]

What can't be done, I still must do --
Forget, if I would live life through.
[tr. Stewart (1915)]

And though 'tis hard to cast a long-worn chain,
Choose any means, but freedom gain.
'Tis safety's only chance, then hold it fast
And do th'impossible at last!
[tr. Symons-Jeune (1923)]

Forbear, while heaven frowns, to fume and fret.
Steel your firm courage to escape her sway.
"'Tis hard," you say, "so quickly to forget,"
'Tis hard; but with a will there is a way.
Here is your chance: this victory you must win:
Whether you can nor no, the attempt begin.
[tr. Wright (1926), "The Poet's Prayer"]

For it is hard, hard to throw aside years lived in poisonous love that has tainted your brain
and must end.
If this seems impossible now, you must rise
to salvation.
[tr. Gregory (1931)]

It's hard to break off with someone you've loved such a long time:
it's hard, but you have to do it, somehow or another.
Your only chance is to get out from under this sickness,
no matter whether or not you think you're able.
[tr. C. Martin (1979)]

It’s difficult to suddenly let go of a former love,
it’s difficult, but it would gratify you to do it:
That’s your one salvation. That’s for you to prove,
for you to try, whether you can or not.
[tr. Kline (2001), "Past Kindness: to the Gods"]

It is difficult to suddenly put down a long love
It is difficult, but you should do this in whatever way is pleasing
This is the one safety this must be overcome by you
Do this whether it is possible or not possible
[tr. Wikibooks (2017)]

It is difficult to suddenly put away a long love
It is difficult, but you must effect this in some way or other:
it is the one salvation, this must be conquered by you
You must do this, whether it is impossible or possible.
[tr. Wikisource (2018)]