Is it ok to imagine having sex weather it’s your partner or someone random

Is it ok to imagine having sex weather it’s your partner or someone random I don’t see my husband all the time as he travels far for work. Before marriage I would imagine having sex with a random person sometimes with someone I know or just random human I imagine. Sometimes it uncontrollable and I can’t stop. I also imagine that the person I’m having sex with is abusive at times. Please let me know how I can stop this and why it’s bad to do this.