I got confused about this sentence because in English you usually say: listen "to" someone/something. The use of the verb "listen" by itself can be found in imperatives, for example. Also, Duolingo translates "escuto" as both "listen" and "hear" but the latter one is not right.
This seems like a very awkward sentence in English to me. Since is often more time-based than because is. It has been 2 months since I saw you last...
But, according to some sources, "since" as a conjunction requires a comma before it:
Well, the link has some helpful examples:
As and since
We often use as and since when we want to focus more on the result than the reason. As and since are more formal than because. We usually put a comma before since after the main clause:
[result] I hope they’ve decided to come as [reason] I wanted to hear about their India trip.
[result] They’re rather expensive, since [reason] they’re quite hard to find.
We often use as and since clauses at the beginning of the sentence. We use a comma after the as- or since- clause:
Since everything can be done from home with computers and telephones, there’s no need to dress up for work any more.
As everyone already knows each other, there’s no need for introductions. We’ll get straight into the business of the meeting.
I'm glad it was helpful. It was harder for me to find a way for why your sentence is outside the norm than it was to show what is the norm. It was a good challenge. It's one thing to "know" yet quite another to be able to explain. But, it helped me as well so this is a win-win for us. :)
por que (why), porque (because) and por quê (that's why), porquê (reason)
Except in Portuguese outside of Brazil there are only two, both just one word: Porque without the accent, and Porquê with.
Still escutar makes more sense as listen while ouvir makes more sense as hear, so porque makes the most sense as because.