Finally getting cucked soon. But getting cold feet, what should I do?

So my gf was pushing for open relationships for awhile. She always wanted freedom to fuck other guys and girls and she told me that in our first date. I was open to the idea but we were too busy for two years to try that.

Then recently she started pushing again, when I realised she wants to fuck other guys I got turned on and she noticed it. We then had amazing sex after that conversation. We then agreed to have a cuckold dynamic instead of open relationships that she really wanted at the beginning. In the long term she wants full open but for now she is happy to try this for me.

In the last week, she was making a lot of progress flirting and sexting and she told me she will be bringing someone soon. My heart almost fell down hearing it but at the same time I got turned on. But the closer it comes to the more I get nervous. I'm afraid of getting cold feet at the last minute, I told her that, she said it's okay if I can't we will pause and try again until I m ready.

What should I do to prepare? How can I handle it better?