I'm straight but... help?

I'm crazy Inlove with my SO for over a year. but I've been having dreams having sex with girls. even just making out. when I watch porn which is rarely I watch lesbians...
I don't want to be a lesbian. I believe in God so it's something that scares me( I know I watch porn while believing in God, I'm not perfect, I sin. ) I pray and pray but I'm just afraid. I'm happily with my SO but something is stopping me especially in my dreams. 
(sorry if I offend anyone somehow)