This is simple:

If you don't have any money to attend events, then you tell your friend you can't come because you can't afford to come. If you are honest with your friends about your monetary situation, you may find that they enjoy having your company around and may pay for You to come with them sometimes, or instead will be considerate and find free things to do (hiking, free Concerts, etc.)

You should find something to do to get away from work at least once a week to balance your life out.