Asked my friend to send me 1 LTC .. gave him an address, but i was bit on drunk and instead giving him my receiving address, i gave him my sending address.
Sending addresses are addresses you've used in the past to send funds to. If you've added labels to them, you can easily check where the coins went. For example, my label can be "sent to Bittrex", in which case the sending address is my deposit address at Bittrex.
So my question is, are these coins gone now.. or i can get these back somehow..
That depends entirely on where exactly you sent them. If you sent them to an exchange, chances are you can find them back there. If you sent them to a former business partner, you'll have to contact him and ask politely to send it back.
the 'sending' address should be the same as a 'receiving' addres. As long as you have the private key to sign a transaction to spend this output, all should be OK, disregarding the terminology you are using....
Core only has the private key to receiving addresses. Sending addresses are kinda like your email address book: they're not yours, but you've used them to send emails/coins.