In relationships, there is often one partner that is more of a giver while the other is more of a taker. This doesn't mean that both people aren't giving as well as taking at times, only that they each lean toward the tendency to do one or the other. This is extremely common and these relationships work out quite well in many cases. Some people actually enjoy being givers. It not only comes naturally to them, but they also find great joy in the giving. They are living examples of the phrase, "It is more blessed to give than to receive".
There are some relationships, however, in which it seems that one person is literally doing all of the giving, while all the other does is take, take, take. This may not bother the giving person in the beginning, but over time, he or she may find that they have nothing left to give. They are completely exhausted and worn out, yet their partner will seem to not even notice the injustice of the situation. In fact, the taking partner might even feel angry because they are no longer being catered to at every turn. This situation is not healthy at all and will not lead to a happy relationship, at least for the giver.
True givers do not give because it is demanded of them. They give because it is in their heart to do so. They give because they have found someone that has stirred in them the desire to give. They give because they want to, not because they are forced to. There is another kind of giver, also, and that is the kind that gives because they don't see enough value in themselves as people. They feel like if they give enough, maybe someone will find them worthy of keeping and loving. They are actually only giving in order that they might receive.
How can you draw the line between a partner who is just more of a taker by their very nature and one who is simply way too demanding? One way is by watching to determine whether or not they are ever giving at all. If you can't see any time that they are laying aside their own wants and needs for their partners, they are overly demanding. If they get angry when their giving partner runs out of the resources, energy, or time to give to them, they are far too demanding. If they want to be catered to even when their partner is run down to exhaustion, this is too demanding. Forming a relationship with a partner like this is a recipe for disaster. He or she will take until you have nothing left to give and when that happens, you will find yourself alone once again.