@Ame,
I can speak from the other side of this. I am a divorced man with a preteen daughter. I had a relationship end for this exact reason, the woman I was dating at the time had trouble with the amount of time I was spending with my daughter.
To be honest, I don't think the steak was a big deal. Your, boyfriend didn't think about how you felt... but on the other hand it seems like to him this was a casual dinner. He made a mistake, but it doesn't seem like a big mistake given the circumstances. Is the steak important to you because it is symbolic of other things you are feeling?
The bigger issue is how to resolve the other issues in your relationship. Dating a man raising a kid is a big deal. I can tell you from personal experience that as a parent your schedule is always flexible... I have canceled meetings with my boss at work when something comes up. And certainly in a dating relationship, the kid comes first. I am sure you accept that.
Now... on the other side of that, you have the right to expect time, attention and affection from the person you are dating. And you should feel special. I think that he should be working out alone time, just you and him, that is sacred and will not be interrupted.
In my experience, it has been easier for me to date women who have kids. I want to say this kindly, but people who have never raised kids sometimes have trouble understanding the flexibility required of parents. Our lives change very quickly and we learn to adapt... if my daughter has trouble at school, or feels sick, or gets into a fight... I drop what I am doing to attend to her.
If you are going to keep dating him without driving yourself crazy, you need to accept this.
Of course you should talk to your boyfriend about how you feel; you deserve to feel special and you need set time alone with him. But you need to be flexible and creative and work with him to figure out how to make this happen.