I want to try something a little different. This fits the "voice" of my current piece but it's not a normal way to write this sort of sentence. Crawling on his belly, left leg dragging in a torrent of heat and pain, “Dear God this sucks,” he approached monkeyboy. Does the spoken section work?
I'd need more context to be confident, but, yes, I think that there's every possibility that it could be a successful nonstandard...thing.
I feel what you're doing here, but stringing the dialogue into the rest of the sentence like that with just commas feels broken. It would feel more purposeful in intent - to me - were you to leave it without a dialogue tag (there's no need for it) and punctuate a little more standardly. Crawling on his belly, left leg dragging in a torrent of heat and pain. “Dear God this sucks.” He approached monkeyboy. I don't mind that the first sentence is a long fragment. I don't mind that the dialogue is tagless. It's almost like a reverse beat. Just my opinion. Others will follow.
I suspect that my tolerance from it comes from a childhood reading Rumer Godden's nonstandard use of dialogue in the middle of sentences. This is somewhat more nonstandard than hers, but hers was nonstandard. Since the rest of the world didn't read a lot of Rumer Godden in their childhood, my opinion may have very limited weight.
The way you wrote it out was the way I originally wrote it. After looking it over, I didn't like the fragment section, but I think you're right, it needs to be separated.
The main problem with the sentence, as other have already alluded to, is that not only does the dialogue tag sound off, it's just plain incorrect. Maybe I'm showing my ignorance, but can 'approached' technically be used as a dialogue tag? Imagine it on its own, in the middle of a dialogue. "bla bla bla bla bla," said monkeyboy. "Dear God this sucks," he approached.
I think that's the main problem with it. I don't think that @doggiedude is using that last phrase is a dialogue tag at all. It's just the last in a series of phrases strung together by commas (wherein lies the "non-standardness" to which he makes reference), but since it comes right after dialogue it looks exactly like a dialogue tag that doesn't work because it doesn't address the delivery of the dialogue in any way.
Yes, I've just come back to say I am showing my ignorance. The fact that he says 'he approached monkeyboy' tells you it's not a tag, but as you say it's punctuated that way so it looks and, more importantly, sounds wrong. Other than that, and punctuated the way you suggest, it's quite an intriguing sentence. Although my personal preference would be for the last sentence to continue. Crawling on his belly, left leg dragging in a torrent of heat and pain. “Dear God this sucks.” He approached monkeyboy and...
Perhaps delete one comma and get rid of quotation marks entirely? Crawling on his belly, left leg dragging in a torrent of heat and pain —Dear God this sucks —, approaching monkeyboy. Although it would look odd if the rest of your writing didn't follow this particular format.