So even though the second word out of our speaker's mouth is "love," it's pretty clear this sonnet is all about a different "L" word: lust. To be honest with you, Sonnet 147 has a pretty bad attitude toward sex. (Even worse than Hamlet's.) The speaker describes his sexual desire as a "disease" that's killing him inside because he can't get it under control, even though he knows he's involved with a woman who's no good for him. The overall message? Lust is super unhealthy and can be destructive when it goes unchecked.
The speaker of Sonnet 147 thinks that desire is fatal—literally and metaphorically.
The speaker of this sonnet has a bad attitude toward desire because he's in a relationship with someone he is totally hot for, even though she has betrayed him sexually.