😤😤😤

My boyfriend and I split bills. He has utilities in his name and I just pay him my half. I paid him 80 last week but a letter came today and he left it out on the side, I noticed the bill was 75 so I've paid the full amount. Not only that but he hasn't actually paid it as it was a letter about the unpaid bill... He usually gets all the bills straight into his online accounts and I haven't been checking the amounts because I didn't expect him to be ripping me off! How do I go about this?