I'm going to take a different approach here. Your stepson is obviously unhappy.
While I agree that you have a DH problem, I also think that you need to help your stepson and look at this just as an issue with a teenage child.
It's today normal for them to be sulky and rude at this age and to want to be in their room for hours. However, he shouldn't be allowed to opt out of family events, sometimes they just need forcing along.
I would look at doing some love bombing on him and building up your relationship with him. Spend time with him, talk to him, make him feel like you care. Teenagers are desperate for attention and connection but they act out as if they don't. You need to parent him and offer it.
And yes, ideally his dad would do this as well but I think you need to do it too. You are in his life as a parent figure and you need to step up to that.
DH is a separate issue. Keep them separate and deal with them separately, but please don't let this young boy feel alone and unloved.
But the way yanbu over the food, your DH in this situation should have made his son something to eat.