‘Stay in touch’ means to keep contact.I will be leaving today to go camping and will be away for a month, but don’t worry I will stay in touch.‘Drop me a line’ means to send someone a note or a message in an informal way.'As soon as you settle in to your new house, drop me a line.'‘A shoulder to cry on' is someone who is willing to listen to your problems and offer advice. She needed a shoulder to cry on and went to visit a close friend.Flickr CC: Kevin Dooley