Can't stay horny 😭😭

For some reason whenever me & my SO are about to have sex it seems like I can't stay wet. And it's like this only in the beginning 😩😭 even when I initiate the sex I can never get wet on the outside. But the inside is like an ocean. To me the outside of my vagina feels like the Sahara desert, but the inside it feels like running water. I think it's something wrong with me & ive talked him this but he always says it's ok. & says it's not my fault. Am I the only one struggling with this? Or what's some tips that I can use?Â