@Lumenatrum,
It depends. I was always taught to remove the clause to see if the sentence still makes sense.
In this case, it doesn't.
"besides" is the only non-essential part of this sentence. it's one of those introductory words like "however," "well," and "in addition" that when used this way always has a comma after it. in your example, the comma belongs solely to besides. it would sound a little funny but you could technically move "besides" to the middle of the sentence or the end.