Beshrew that heart that makes my heart to groanFor that deep wound it gives my friend and me. (1-2)
Wow. This dude must really be heartbroken about his mistress' cheating ways. Why else would he drop the biggest love cliché on us here? Basically, he's playing off of the idea that lovers get wounded when Cupid shoots an arrow in their hearts. But, here, the speaker sounds pretty gross when he says he's got a "deep wound" that makes his "heart to groan." Eww. He makes it sound like his heart is a wounded person rolling around in agony. (FYI: that's a literary device called personification.)
Is't not enough to torture me alone, But slave to slavery my sweet'st friend must be? (3-4)
Ever heard the expression "I'm a slave to your love"? It comes from the courtly love tradition, where lovers act like the willing servants of their beloveds. That's basically what the speaker is saying when he accuses his mistress of turning him and his friend into a couple of pathetic love slaves. But, there's something ugly and menacing about the accusation, especially because he introduces the idea of being "torture[d]" and the literal concept of "slavery." We also notice that the speaker seems interested in sticking up for his friend, even though the guy has been hooking up with his mistress. When he says she's turned his buddy into a "slave to slavery," he makes it sound like his buddy is an innocent victim.
Me from myself thy cruel eye hath taken, (5)
We've all heard lovers run around saying stuff like "I'm yours" and "I belong to you," right? Here, the speaker acknowledges that he belongs to his mistress, but not willingly. When he says she has "taken" him from himself, we get the sense that he feels like he's not even his own person anymore because she totally owns him.