Ended a situationship and feeling bit sad … anyone that is also going through it give me some tips?

I knew going into it, it was never going to be anything serious, he wasn’t a potential for me but I still ended up developing feelings and he grew on me.
It feels like a breakup and I feel bit sad, although it ended mutually it got messier then I liked it to be near the end.
We both agreed to be friends but why does it hurt even though I knew it was never going to be anything other than casual?
Ended a situationship and feeling bit sad … anyone that is also going through it give me some tips?
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