so i want to make some chocolate cupcakes for v day with a raspberry buttercream, i was thinking of filling the insides with some kind of chocolate fudge or chocolate sauce filling what would work better and does anyone have a recipe that will hold up in the cupcake and go well with raspberry or is there something else i should fill it with that would work better with raspberry buttercream 

It's called ganache.  Chocolate melted with cream and flavours.  It has a soft creamy consistency at room temperature.  Use google to find recipes.