Feel for you! I am not in your situation but I have been in others where I felt stuck, wanting to change lots of things but feeling like they all interfere with each other.
Since you asked for suggestions, here are mine. First, think about your relationship with your son, because his well-being is the most important of your responsibilities. How would moving away affect that? Would you be less likely to see him? Perhaps not, if you see him regularly for scheduled times. Would that change when he's older? If he has school concerts, soccer games, plays, etc., would you drive the 4 hours to see one? Also, what is the likelihood that his mother and he will move somewhere even farther?
Second, I'd give the accounting a bit more time. Pretty much any job is boring at entry level, so wait and see whether more advanced work is more interesting. Meanwhile, investigate alternative jobs you could apply for, and consider how they compare in terms of pay, chance for advancement, location, bikeability. If you turn out to like accounting once you get beyond entry-level bookkeeping, would you drop the 8.4-miles-away job and do accounting only? Would you have the possibility of opening your own business some time in the future so you could choose your location?
Third, think about the commuting. How does the speed of bike commuting compare to driving in your area? Are the jobs you'd be looking at suited to biking? (Or, put another way, how much does requiring a bicycle commute restrict the jobs you can look at?) How important is time vs gasoline as a commuter?
So, no answers, just questions for you. Good luck!