You aren't stuck - you can leave. You are essentially supporting 3 extra people on less than double your income (if he makes way less), so surely you can support 2 on your income alone. Work out a budget and get yourself out.  Your son/daughter and you deserve better.

FEAR is what keeps people stuck.  Address those fears and the way out will be clear.

Start looking for a 1 bedrrom where you can turn a dining area or other area into a bedroom.  Put your stuff in a closet, give kid the bedroom and you sleep on the couch if you have to. 

this will only get worse

Kick his lazy mooching butt out. He is an anchor dragging you down.

You are not stuck.  You are making the CHOICE to remain in this relationship. 

I was a single mom.  When lived in NC, it was tough because teacher salaries were so low there.  Once I made the CHOICE to move back to NYC, things changed drastically. 

If you and your son moved into his home, move out.  If he and his kids moved into your home, give him a move out date. 

This is not the relationship for you.

Look into it

Your not stuck, you have decided to stay.

Now you can also decide to leave. It is totally up to you.

Get your kid away from the skids. It will drag him down. He will see how their lazy asses get away with stuff and decide he should do the same. You will make it on your own. I lived on less than $20,000 a year with 2 kids in the late 90s in an area where most people made 50-70K. You will survive and be better for it and so will your kiddos. You came to the right place for advice.  These ladies will tell you how it is. Dont let a lazt man and his a-hole skids drag you down.

If you think it bad now wait till the sk get into there teens. Just sort your finances out. Get out of this relationship if your not happy. Your bf sound like a bit of a dead beat anyway. If you plan before you leave. Your be okay. 

Leave because you aren't doing anyone any favours by staying in an unhealthy situation.
 

I imagine it is quite terrifying to imagine leaving. Often we get ourselves into situations that are harder to get out of than they were to get into and the discomfort of the exit is so great, we stay. But. You already know this. If you choose to stay longer, your reasons for wanting to leave will grow. Your unhappiness will deepen. More time will have passed and exiting later will hurt everyone, including you!!, more than exiting now. Just go. 

Your SO isn't respecting you and he is screwing up his kids by not being even a semi-engaged father. You can do so much better than this. Rip the Band-Aid off, girl! You will feel such relief when it's done that any discomfort you feel in the process will be of no consequence.

The hurt your SO and his kids will feel isn't going to be less if you drag the relationship out longer.  You know it's time to leave, and from what you've written it sounds like YOUR child would benefit from getting out of the situation.  As a PP said, rip the bandaid off and get it over with.

Not once did I read the word 'love' in your post. Is there love in this relationship? I read the words stuck, depressed, angry, irritable. You really need to take baby steps and get out of this relationship. The next thing you know 30 years will have passed. If you're the cash cow that isn't going to change. These SKs will become teens, then adults, and your problems will multiply to the nth degree. Take it from one who knows.

and then get the DUCK out of there.

Seriously, you need to grapple with that fear demon that has practically paralyzed you. Its coming up to the end of the year - make a promise to yourself that you will start the new year with either a place empty of him and his spawn, or you have a fresh new place of your own. Often its easier leaving and starting fresh than trying to get a deadbeat out of your space.

BUT whatever you have to do - do it! Think about your child, not HIS children. Dont think about pain YOU are going to cause by leaving, think about the freedome and happiness that you and your child will experience being free of deadbeat moochers!

Your SO is a jerk, his kids are jerks. It wont get better, the pig wont turn into a prince.