If IANBU.. why is everyone (including DP) making me feel like I am?
As LoveInTheTimeOfCorona and others have said, it’s classic abusive manipulation. They are trying to push you into doing something you don’t want, and if you concede ground and don’t stand up for what you need now, you will be pushed further and further because once they know they can, the dynamic is formed and they will use it.
Your ‘D’P is sulking. Another abuse tactic to get what he wants. He believes you’ll give in. He’s not putting you first, and he should be. In fact right from the moment he said ‘no’ to his family and added in the suggestion it was ‘because you would be too stressed’ he’s demonstrated his disloyalty to you and loyalty to them. Had he said no without adding that, he would have sent them (and you) the message that he and you were a team. He indicated the opposite.
I don’t know if you should marry him. Pity you’re already so far in, because if this was happening before DC it would be a good time to properly lay it on the line and consider splitting up.
It’s about boundaries. You have the right to say no, and for that to be respected. You’ve said no, it hasn’t been respected, and that is a huge red flag.