You can only give what you possess; but if you give all that you possess, then you will have nothing left for yourself.
Giving to the point of self-detriment creates frustration, which leads to angst, which leads to anger. A person who feels empty will give grudgingly. Eventually, they will refuse to give at all. They may start to keep track of all that they do and use those deeds as ammunition against the person to whom they have given. They may start to demand things in return for even the smallest acts of kindness.
At this point, the act of giving will have ceased to be a gift. At this point, the relationship has become one of convenience. Both parties are in the relationship because they need something from one another. Respect, love, and sincere appreciation have taken a back burner to need. Any relationship in this condition is troubled.
Keep in mind that before you can support another person, you have to make sure that you are well taken care of. There may be times that you give out of an abundance and there may be times that you give out of your emotional reserves. Learning to maintain a balance is necessary. You will want to ensure that you do not run empty. And it is ideal to abide in such a state of balance that you do not have to use your emotional reserves.
The key is to learn how to monitor and manage your own needs.
For, if you do not have what is required to take care of yourself, it is going to be impossible to truly care for anyone else. You cannot give that which you do not have.