There are people whose sole purpose is to come into your life to teach you a lesson.
You may not know it. They may not know it.
And when you have learned whatever it is you needed to learn, they make a clean exit. Or sometimes they make a messy one. Either way, this person will eventually disappear.
Take in what they’ve taught you. Appreciate your time with them for what it was. It’s okay to still be happy about the memories you may have with them. It’s okay to even be a little (or a lot) sad about them leaving.
But it’s equally important to move forward.
He or she has served their purpose and now it’s time for you to turn the page.