Sleeping over at my boyfriends

I am a senior in high school and my boyfriend graduated in May and is working full time, but as much as I would like to sleep over at his house, I know it’s wrong and I shouldn’t do it. My mom is okay with it but he just gets aggravated and ‘because I don’t want to’ or ‘i need to go home’ isn’t cutting it with him anymore. What should I say because he thinks that I’m not wanting to be with him (after over a year together).