Military Boyfriend

So my boyfriend is in the military, meaning I see him once every 4-5 month(ish) however, every time he comes home and we have sex it hurts me so bad like losing my virginity all over again. When he comes home it's only for about 5 days and I dread having sex because it hurts so bad. I'm convinced it's because he's gone for so long and maybe I shrink back up? Idk. Any advice on how it won't hurt me anymore? Or why it does?