should I apologize to the five year old and his Mom (my fiance)?

the long and short of it is this.. her 5 year old son will not sleep through the night because until they moved in with me (this past June), he slept in bed with her. Now, he wants to be in our bed. He wakes up in the middle of the night screaming and yelling for her. He then comes down to our room and wakes us both up. Once I'm awake, I'm awake. Needless to say, I was really tired the other morning and I snapped at him. She is TOTALY pissed now, but I still don't think I'm wrong. He wasn't listening as usual and I guess I just snapped. I didn't curse at him or anything, but I did tell him that I was sick of this, and he was not sleeping in our bed anymore. I guess you could say I was yelling, but that's debatable. Anyway, she's not talking to me now. He has a behavior problem called spoiled kid syndrome, so simply asking him to stop doing something doesn't work. She says I "started his day badly". I say he started it badly on his own by choosing not to listen. Any advise here would help. BTW, I would normally just apologize and be done with this, but I'm pretty firm on this one. I want him to learn.