When and how do guys become certain of who they want to marry?

I know every guy is different, but I want to hear your opinions and personal experiences.

Over the past couple of months, my friend has been dropping some serious hints about marrying me.
I’m shocked because we have only ever been friends, and I never thought someone could feel so strongly for someone they have never had any romantic or sexual relationship with.
This got me thinking about the complexities of individuals and relationships.

When and how do guys become certain of who they want to marry?
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