Abstaining from sex after cheating

Long story short my friend got cheated on and took her bf back. He apologized they talked it out they’re in a good space. She wants to abstained from sex for a while just to get her emotions in check. She’s just not 100% trusting and comfortable with having sex with him again. She’s not punishing him btw. He keeps asking her for it. So what’s a nice elaborate way to say no and why. I know some will say just say no and leave it at that. But she wants to explain so he can understand the hurt behind her decision not to have sex just yet.