After 4 years together, your DP really should have considered your feelings in this, and it doesn't sound like he did at all.
I'm guessing OP, that you may have been planning a meal for the two of you, got some nice bits in that you wouldn't ordinarily, or perhaps planned on getting a takeaway, and now you're left on your own. It's not the same cooking for one, that's if you bother.
You say he's done this before OP, which most likely means he'll do it again in future, and you'll feel put out by it again.
If you've never said anything before, I'd mention it to your DP, saying that you understand his DC is a priority in his life, but that doesn't extend to dropping you whenever DC calls (illness etc excepted). It's rude and inconsiderate of him.
If you've raised it previously, and he's continuing to behave this way, you already have your answer, and need to decide whether or are happy to live like that, especially in future if you move in together.