Clear communication and consent at all stages of sex is key. Talk to your partner before having sex and say there may be things you’re okay with and not okay with. This sets up the conversation during sex to be normal, expected, and not about hurting anyone’s feelings.
Just as it is appropriate and healthy to say to your partner “I like it when you…” or “I don’t like it when you…” it is also appropriate and healthy to tell your partner “I’m okay, keep going” or “I’m not okay, please stop” at various points throughout.
Don’t expect your partner to know how to communicate like this, so model it for them before and during sex. Finally, keep in mind that if you decide to tell them to stop, it makes sense for them to feel a little disappointed and that’s okay. You are not responsible for their feelings, only yours. So keep communicating, and know that stopping if you or your partner isn’t comfortable is normal and OK!