Boyfriend no longer wants to have sex.

So my boyfriend and I have been dating for eight months now. We knew each other for three years before we started dating. So we've been living together for a few months now and when he first started coming down and staying here, we would have sex multiple times a week. And now that we've moved out to our own place it went from multiple times a month, to just two times a month, to just once a month, and now we have not had sex for an entire month. I have brought it up a few times and told him that's it's an issue for me and he is completely nonchalant about it and just laughs it off like it's a joke. But I don't think it's a joke. He is 100% an open book. I am allowed to go through his phone whenever I want to, I can use this phone whenever I want to. When I get on his phone, I look and there's nothing that would cause me to be suspicious. I was cheated on in my previous relationship with my daughter's father so I feel like I can pick out the signs and can tell when someone's being shady and suspicious with their phones because my ex was always shady with his phone. I don't think we have any serious problems, the only stress we have is money and job stress. But I don't know what to do. Before we moved in together he was always the one who initiated sex, and since we've moved in together, I've been the one who has initiated. I have started to slowly back off and I haven't even really wanted to try and initiate anything because I don't want to deal with the embarrassment and hurt of being rejected again. I just don't know what to do and I was hoping that somebody else had gone through this and had some advice?