I wouldn't use this poem as a "Sweet" poem - it's actually a poem begging a lover not to leave. Most historians attribute Shakespeares sonnets to a love triangle that was believed to exist. It was believed shakespeare had his wife, though he also had a gay lover (who he loved most) and the gay lover was getting married to a dark haired women. Shakespeare didn't want the dark haried women in the way, but wanted the blond man to stay his secret gay lover alone. In this, he begs his lover not to go to the "rosy lips" and to stay with him because their love is apparently "true and eternal", he even jokes that if their love be less than the love for the other women, then he "never writ". Even if the triangle "theory" be incorrect (despite the evidence), this poem still speaks of a lover begging what they believe to be their soul mate to not cheat and to not leave for a whore.