Feel like boyfriend don’t love them

Does anyone else feel like their boyfriend don’t love them even when they actually do?? I’m terrified my boyfriend is going to leave or cheat on me and he swears up and down he loves me and he’s not. He says he wants to marry me. He’s bought me a promise ring too. It’s just that something in my head is scared he don’t love me and that everything bad is going to happen. Why do I feel like this?? How do I stop???