"Get a life" may be a crude and harsh way to express it, but it was the best advice I was given (gently by my mother-in-law) when I was a young 'golf widow' (I married into a family of golfers) and I used to mope around miserably and bleat about my husband being on the golf course on weekends, making everyone around me including my children unhappy too.
What it meant to me (when I got the message) was that I was no longer dependent on something or someone else to make me happy (or blamed them or it for my unhappiness), but I simply got on with my life and made the best of it. And enjoyed it!
Although it didn't make things right (he was being selfish), I started enjoying my independence, harmony returned to my home, and not long and it would be a case of "What do you mean you're not playing golf this weekend?! I'm off with so-and-so to do such-and-such. Bye!"
So to me being told to "get a life" was a good thing.