So, Sonnet 133 is all about a torrid little love triangle between our speaker, his mistress, and his BFF. Obviously, there's going to be some talk about sex, right? Right. But, the funny thing about this sonnet is how our Speaker doesn't come right out and directly accuse his mistress of sleeping around. Throughout the sonnet, he uses "double entendre" (words or phrases that have two meanings) in order to slip in a bunch of dirty jokes about his mistress. Whenever he does this, it's usually so he can imply that she uses sex as a weapon to keep both guys in her clutches. So, the Speaker's sneaky emphasis on the physical part of the love triangle makes us wonder if the relationship has anything at all to do with "love." Maybe he's just ticked off because he can't control his sexual desire for his mistress, despite the fact that she causes him a lot of emotional suffering.
The speaker of Sonnet 133 makes jokes about sex because he doesn't want to admit that he can't stop himself from sleeping with his two-timing mistress, even though his relationship with her makes him miserable.
The green-eyed monster strikes again. The speaker doesn't care if he can't have a sexual relationship with his mistress—he just wants her to stop hooking up with his friend because it makes him feel jealous.