I'm going to let a girl cheat on her boyfriend with me
That sounds like something that could end up causing a lot of hurt and anger.
I need to make her like me and I think she likes me too much, if I refuse to hook up with her, she might hate me
Even if refusing her will cause her to hate you, you still should not have sex with someone in a relationship with someone else. If you have sex with this girl it could destroy her relationship with her boyfriend.
I'm very responsible about this. I'll use a condom and I won't text her after that to make her boyfriend jealous.
Coaxing someone into cheating is not a good thing. If you want to be more responsible, let her be angry with you. Do you really want to get involved with someone who treats her boyfriend so poorly? One day the shoe might be on the other foot.