What just happened?!

It all started with I had lost my phone (I don't all the time, I'm a mess) and after searching for like an hour and having my bf calling it I asked to borrow his phone for light because I thought it was being the sofa and he refused to let me borrow his phone and he said no, go to bed and I'll find it for you and I was like no I can't go to bed because I'm stressed out about my phone, I need it for work tomorrow. And he refused to let me have his phone and I continued to search for my phone and he started making remark like "who's messaging you. Oh you're so popular today" because it was beeping a lot (from getting messages) and I was like "are you serious, it was my birthday yesterday" and he said "yeah yesterday so why do they write now" I told him he was being ridiculous and then he said I was ridiculous for not letting him look for my phone by himself and I asked him why he was being so shady and acted like he wanted go through my phone because I have nothing to hide. In the end I got so upset I just yelled at him "fine look for it but if you go through it you'll spoil your birthday because that's all the secrets you're going to find on there" (his birthday is in two weeks and I've ordered a bunch of stuff for him) and I stormed away. I eventually found my phone in our bedroom where I'm now and he's still in the living room. I don't know what the f happened in there. I'm still so upset. I know his ex cheated on him but that was years ago and I don't know why he accuses me of cheating on him after four years together. It's not the first time he accuses me but this was so extreme. I don't even know why he is with me if he thinks I'm cheating and every time I tell him that he insists he doesn't think I am and yet this happens?