Idea of Selflessness

What is Selflessness ? Can anyone be unselfish 100%. Our cynics definately will disagree. Well, they are right in one way if we consider everyone does everything directly/ indirectly for one's own happiness. Thats each human's aim and that can be considered selfish. One common way to define selflessness is to say that one is happy on seeing other's being happy. That one does for other's good and fulfills his need to be satisfied . But what do you do if no-one wants your help cause it guilts u. Well simple leave that person i guess cause most imp is that person's happines but do you actually do? Loosing a relationship that took years in the making and just now , you leave that person. I would say leave the person , let the person come back to you if the person is happy with you , if not , that means it wasnt meant to be and she is happy with someone better than you . But dnt forget what you did was selfless and is ultimate sacrifice one can do in life. It doesnt mean that u put ur life in other person's hands . U control ur life , noone else does but u just be happy by spreading happiness and dnt expect anything in return other than a smile . But one dilemna one faces is when do your actions cause hurt even if your intentions are for the good? How do you realize and what to do then.? Thats a tricky question. One way is to simply continue without realizing but when ur confronted , u will hurt for sure. Better is to see if things changes , then leave that person alone , if she is happy with u , she will come back , otherwise she wnt. True selfless people will be happy both ways , but is anyone upto the task ??? Plz send ur ideas