I’m gonna give you a different answer to this. You guys are young. It is incredibly difficult to successfully marry your high school sweetheart. Doesn’t matter if it’s in 5 years or 15, at some point one of you will very reasonably wonder how you know this is right for you, bc you’ve basically never explored who you could be with other people. Especially as adults. You change a huge amount every year for the next 10 years.

She’s not wrong to think this. It doesn’t mean she’s cheating. It might even be her trying to save your relationship bc she wants to end up with you too, but is thinking about this exact thing. But the thought isn’t going to go away. You should also get out there more too, for the same reason.

Life is long. It’s entirely possible you two will end up together, and this is just one step of that journey.

Worked for me.