You could go the direct route:
“ He didn’t pay, we should blame him.”
Being this direct emphasizes the seriousness of said allegation.
Or you just could say: “He didn’t pay”
↗️ This sentence implies that you and reader/listener know that the offender did not pay and therefore conclude that said offender is the person to blame.
Your example features 'FANBOYS' (or coordinating) conjunctions (for, and, nor, but, or, yet, so) and is thus a compound sentence, not a complex one.
Compound sentences join sentences of equal standing.
Complex sentences feature subordinating conjunctions (e.g. although, since, because, etc) and these are the ones that feature a main clause and subordinating ...
The definition of main clause is simple enough.
"A clause that can form a complete sentence standing alone, having a subject and a predicate." [Oxford languages]
"Main clauses make sense on their own. 'I like bananas. ' is a simple sentence which is made up of a main clause." threschoolrun.com.
There is a distinction between ...
One understands naturally, so to speak, that "only" means "did nothing else but"; however, the naturalness is to be placed on the count of the logic of what the remainder of the sentence tells us, not the position of the adverb, this being so because in this position one possible interpretation, "he watched TV but watched nothing ...