At one point in the sonnet, our speaker's dramatic way with words conjures up an image of Christ's crucifixion. Wait. Why the heck would he do that in a poem about some torrid love triangle? Because he wants to give us a vivid sense of his suffering and torment, that's why. But, even though we get a clear sense of the guy's pain, we might also begin to think of him as a martyr here (if we haven't already) and we wonder just how effective the biblical allusion really is.
Lines 7-8: This is where the speaker says that being "forsaken" (abandoned) by his mistress and his BFF is a "torment" that must be "crossed" (thwarted or prevented from happening). Hmm. The words "forsaken," "torment," and "crossed" sort of jump out at us and make us wonder if this guy actually thinks his pain and suffering are worse than the crucifixion of Christ. So, we take another look and realize that… yep, dude really is comparing getting cheated on to being crucified.
Like we've said before, the word "crossed" has the word "cross" in it—as in the kind of physical structure that people get nailed or tied to and then left to hang from until they die a very slow and agonizing death.
Then there's the word "forsaken," which shows up in some very famous Biblical accounts of the crucifixion. When Christ feels abandoned he shouts "My God, my God, why have you forsaken me?" (Mark 15:34).
(And, in case you're wondering, yes, Shakes knew The Biblelike the back of his hand.)
Notice how totally casual the speaker is about dropping a crucifixion reference on us? It's as if he thinks it's totally normal for him to just toss out the idea that his steamy love life is some kind of religious event. What's up with that? Does this give us a better sense of his emotional pain and suffering, or does it make us think the guy's a little over-dramatic? Go to "Themes: Suffering" if you want to think about it some more.
P.S. Our speaker makes a similar move in Sonnet 44. Check out how he complains about how bad he feels knowing that his mistress and his friend are hooking up with each other: Both find each other, and I lose both twain, / And both for my sake lay on me this cross(11-12).