Homemade Frosting- how long does it last?

Homemade Frosting- how long does it last?

I made some buttercream frosting a couple days before Christmas to decorate cookies. I was cleaning out my fridge today and found what was left of it- there is still a fair amount left, but I have no idea how to tell if it's still good. There isn't any visible mold, but around the edges of the frosting there seems to be a liquid substance. Do I just chuck it to be safe? The main ingredients are butter, powdered sugar, vanilla, and a little bit of milk. It's been refrigerated the whole time. I guess it's mostly the milk that concerns me.
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Finally!

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