People screw your life all the time. The most painful thing is people you care so much screw your life all the time. The worst part is you still care for them.

You befriend with them. You support them. Your kindness shines upon them. And they are just all that. Receive all your kindness with pleasure. Feel warm and safe near you. And snaaappp... after that. They're gone.

Yes my dear, you are 'only' a very good friend when they were in trouble. You are the most suitable person for their worst condition. That's all. Period. They don't need you in every time of their life, most of their life.
Or maybe, maybeeee... still unlikely but maybe they are just scared of you, cause your light shines so bright upon them.

Pity on you? True. Sure.
Bless on you? You may say that.
Curse on you? Likely...

So just be prepared because someday one day in the near future, they will be back asking and begging for your help.

So just be patience. If you can't handle them, withdraw yourself, let them go and let you live your life with other persons who put respect on you, love you unconditionally. Maybe that other persons are your truest friends.