No one bound you into helping these people. That was your choice. Did you tell them at the outset you expected compensation? Did you explicitly state you needed help now? Did they say they needed your help?
You shouldn't do things for ("help") others expecting reciprocation. That sets you up for disappointment. You help others because it makes you feel good, or because you can, because you think it's an essential part of your identity. If you help someone beyond their capability of paying you back- should they feel torn-up inside for the rest of their lives trying to pay you back? I don't think so.
If this is a long-standing relationship, however, of course a "betrayal" of this sort will probably trend it towards dying (all relationships need to be feed and all that stuff). And that's the price you'll both pay- the decline of a relationship- for lack of support so to speak.