I love how Molly says this. I don't necessarily ship Johnlock, but I believe they truly love and care about one another and Sherlock doesn't want to trouble him by showing there is something wrong.
Playing mind games and playing with someone heart is SO wrong. You want him/her tell them and do something about it... "punishing them" for past mistakes is so wrong. Case of I don't want him but don't want anyone else to have him. Don't be selfish.