What should I do if I think my boyfriend is stealing money off me?

I put £100 in my cupboard and I know for a fact I only took £20 out so that would leave me with £80 right? I do live with my family but we can leave money around and be fine we completely trust each other. But I checked today and I only had £60 and I have to think it but could it be him? I also have £5 laying in my room which I went to go and get yesterday and couldn’t find it so I ask him if he’s seen it and said no and helped me look as I didn’t just want to leave it but I went downstairs and he shouting that he found it where I’m sure I looked.

What should I do?