If that thise men that lovers hem pretende,
To women weren feythfull good and trewe,
And dreden hem to deceyven or offende,
Women, to love hem, wolde nat eschewe;
But every day hath man an herte newe:
Yt, upon oon, abide can no while.
What fore ys it, swich a wight to be-gile?
Source, in full
If those men who to be lovers pretend / Behaved more faithfully and did not lie, / And dreaded to deceive or to offend, / Then women might not choose to pass them by. / But each man's heart's a fickle butterfly / Which can alight on one just a short while. / Can it be wrong in this case to beguile?
Notes from Wikiquote
"The Letter of Cupid", line 267; vol. 1, p. 83; translation from Thelma S. Fenster and Mary Carpenter Erler (eds.) Poems of Cupid, God of Love (Leiden: Brill, 1990) p. 191.