This is a communication issue. You need to be transparent about your finances and what you are willing to spend money on.

If your income is a gray area, it's going to be incredibly difficult for him to accommodate you and your needs.

I think it's important for your future's sake to not hide things from him. Pretending you're not hungry is not an effective way to tell him that all of these outings are straining your budget.

With that said, you may want to look into why letting him cover you is so difficult and seek to find a compromise on this.

Maybe you don't go to as many ski trips, but you let him pay for most of your meals?

At the end of the day, you are a team and need to be able to effectively tackle this together. That can only happen if you're straightforward and honest with him.