The eighth commandment: You shall not steal. The negative meaning is that you should not take what is not yours.
But the Westminster Shorter Catechism is great in that it tells you what you should do instead.
Question and Answer 74 say that you should lawfully procure and further the outward wealth and estate of yourself and others.
Basically, if you work and buy something, that is good and even required by the commandment to not steal. Also, if someone gives you a gift, you accept it graciously. That is also lawful gain for yourself and your estate.
When someone is co-dependent, they want to give everything away, never accept gifts, and they not only rob themselves of their own rightful possession of things, but they also rob their families as well.
The answer to question 75 affirms this sentiment:
The eighth commandment forbiddeth whatsoever doth or may unjustly hinder our own1
or our neighbour's wealth or outward estate.2
Those footnotes link to the Scripture references. But even if you steal from yourself it is still theft just like suicide is still murder.
Overall, Commandment 8 discourages believers in Jesus to simply not be preoccupied with possessions. If you don't have something, then work to get it. If someone gives you something, then rejoice and use it to God's glory. If you do have something, then be content. If somebody needs something, then give them something, of course making sure first that it is yours to give. God wants us to not obsess over our possessions but to simply live and not rob ourselves of the graces he has given us either directly or through someone else.