Get your own place.

A long distance relationship is not real life. It does not give you the chance to truly know someone, their kids, and the whole dynamic, on a day to day basis.

Get your son out of that environment and date your BF but don't live together.

I agree with hereiam, you should getyour own place & continue to date your BF.  If neither of you had kids it would be overwhelming enough to go from LD to living together, adding kids into the mix only makes it that much harder on everyone.

Pay attention to how your BF handles the way his DDs treat you & your son.  Kids don't just launch & stop causing drama, especially when it's allowed to happy because the BP does nothing about it.  If he's a Disney daddee do yourself a favour & run!

Everything depends on how your BF handles what his daughters are doing.  Is he putting a stop to it or dismissing it?  Start how you want to continue because what you accept now is what you will be dealing with forever.  Growing pains are normal but someone who refuses to see that he has to participate in resolving them is always going to be a hands-off parent.  You can be slow in unpacking everything and see what happens.  His place can very easily be a temporary "way-station" to your own place if the area is one that you like.  There is nothing wrong with citing the age difference in the kids as a problem and living separately until they go to college.  But don't wait too long and do too much damage to the relationship.  You are in a good position to do it in a loving way now.

Long distance is not a good gauge to a relationship, move out

What exactly did his girls do?  Did he prepare them for you and your son moving in?  Did any of them have to give up a room?  

I've learned that you really don't know someone until you live with them. When they are in their most natural, vulnerable, and every day state of being. That's when you see all the habits, good or bad, their little quirks. You probably didn't spend enough time/days with him to see how he parents and interacts with his daughters on a daily basis. You went with what you saw for the moment and assumed it was like that all the time.

If you feel this way 3 days in I think you should have a heart to heart talk with him. Give the living arrangement a deadline and if things don't improve consider getting your own place.

I don't have a son. It's just me. But I did move over 2000 miles to be here where my Dh is now with the girls... It was terrifying... There are definite questioning moments. And as users said above, it's been a learning curve for us both being in close proximity. Even talking basically all day, every day, skyping and flying out to visit each other for over a year and a half. It was just different!

I like what someone suggested about finding a small apartment and continue dating for a bit. or even stick it out and just make an adjustment. EVERYONE, both of you the kids, are going to have to adjust and make changes for this to work. new people in the house is a change for everyone and just might take some time

What little Bi****s,  there wayyy to old to be treating your son any type of way hes 8!   I agree get out of there and get your own place or tell your BF like bro get these girls or we fighting LOLLL kidding...   and on a side note teenage girls are visious !! have everyone get to know eachother wayy better before there under the same roof you dont want your son to end up being bullied by perople hes lives with its going to cause resentiment between everyone. 

GET OUT NOW!!!!