Insecurity

Do any of you experience a monthly insecurity that makes you feel like you s/o will cheat or leave you for someone else so easily? It makes you feel like hes not all yours? Every month i get this feeling like my fiance can be led into temptation by another woman. I start feeling like i dont love him or that i cant trust him. We have been together for 6 years and he always tells me how much he loves me and how excited he is to marry me. But i am always having dreams that he is leaving me for a close friend or that he will go have sex with someone else on his business trips.