I think about cheating on my boyfriend
That's not good. Why would you want to cheat on him?
Yes, I want to try it with another guy
If you think that you want to cheat on him then you should leave him. It's never right to cheat on someone and will only cause them terrible pain. Have you thought about talking to him about this?
So you think guys shouldn't have more than one partner
No, unless there is mutual consent on all parties I don't believe people should have multiple partners. How would your boyfriend feel if he trusted you so much, and you slept with someone else and gave them your all? I think it's best to not go with this action.