Partner Misappropriating my Funds

My boyfriend supports two households: me and his daughter, and his ex wife and her 2 sons from a previous marriage (16 and 22).

First off he supports them because she does not work ("back problems"), and he still wants to make sure that his stepsons are taken care of- he's the closest thing to a father that they've ever had. (Because this woman is selfish and a little screwy. I don't always agree with it, but I understand why he does.)

Now. I lost my job before i got pregnant, and when our baby was born 3 months early, I was not able to look for a new job. She was just discharged from the hospital a couple weeks ago. Because if this, money is tight. All the time. Our daughter is 3 months old, so it's even tighter what with formula and diapers. At this point, my diet consisted of oatmeal and ramen. So I applied for food stamps for myself and my daughter. I recieved an EBT card 3 weeks later. I don't have a working vehicle right now, so if I need to go to the store, he will go for me- plus it's a lot of work trying to get a ride from someone, with a baby in tow.

I originally wanted to be the first to use this card. I tried to stick it out until I could get a ride. But my kitchen was never very full to begin with, and I was desperate. So I handed it over with a grocery list, asking him to bring me the reciept because it will have my remaining balance on it. I also asked him not to use any of the funds to benefit the other household (in a text, in writing).If they should benefit from food stamps, then they should sign up themselves. The library 3 miles up the road has someone from the food bank come in once every month or two. That's exactly where I went 3 weeks ago.

When he came back, he said he just picked up essentials and whatnot. Granola bars, applesauce, formula, milk, coffee, etc. Basic things. No biggie. He even brought back the reciept.

But then , out of curiosity, I decided to check the balance.

$15 less than the reciept.

I'm angry. And betrayed. I specifically asked him not to do this, and he did. He just broke the transaction into two, and figured I wouldn't notice. This is specifically my money. I specifically asked him not to spend it a certain way. Why should the grocery money for me and my daughter be spent for a kitchen I have no access to, and a household that doesn't even like me?

Next time, I will not be giving him my card, no matter how desperate. But beyond that, I'm not really sure what to do, or how to approach this without starting an argument or a sulk fest.