You are being used, however... His purchasing habits sound as though he grew up quite poor (lack of storage space or limited capital are the two reasons for aversion to bulk-buying, both caused by poverty, and you develop 0 long-term planning skills when you have 0 capital), so it's likely to me that you're fighting a battle with both his conscious ("I don't want to pay to go out to eat, we've got food right here") and his subconscious (hundreds of hours of stressing about money). Does he contribute measurably to the bills and fixed household expenses?

If it's genuine financial anxiety brought upon by a heartfelt fear of not being able to sustain himself or provide for his future, then I think you should address that by scheduling some time to discuss your future with a financial planner (you should do this anyway at your age, regardless of whether you ultimately remain together). If he were investing money diligently toward your future together, then I think you'd feel a little less gypped about his miserly tendencies, and he'd be able to channel them into something productive.

Have you spoken to him about this at all? Not so much the financial aspect of things, even, but the fact that you feel genuinely hard done by and taken advantage of; you're the one not only doing all the leg-work to plan fun stuff to do as a couple, but also then bankrolling 90% of it.