I know I'm from the old school. But here is a message for the new-age people grappling with the issues of relationships. Don't tear away the bond suddenly, turning the other one as a redundant item. Talk it over and transform it into a milder bond, put your case gently. If the person isn't suitable in the new phase of life, don't make him/her a dark angel at least. Transform it into friendliness (it's possible by the way—with open heart-to-heart talks) and drift away gently. There aren't bloody cleavages in this, leaving one party broken and the other one guilty. Why run away? If you run away in haste, you will carry lots of pain with you and this will draw you into similar circumstances with a different person in future because of its sheer momentum in your system.
I know ex-lovers can still become possessive and take your friendliness and nicety as willingness to come together again. But that's just an impulse at the initial time. If you maintain your courtesy, friendliness, dignified respect, impersonal aloofness and sufficient detachment (that separates friendliness from a love relationship), the other person will get the message very soon. Then you won't have a big block list in your phone. And blocks in our phones are merely forced attempts at negating a still nagging reality, an artificial attempt to bury a pain. It stands for either a feeling of victimhood or guilt.
If you drift away gently, allowing him/her to see you walking away, sometimes looking back with a friendly smile, sometimes waving a bye, then he/she won't feel cheated or broken or dumped. Why leave someone broken? You have every right to proceed with your choices for the future. But why run away? Because if you run away, those same circumstances follow you in a similar relationship with another person. So walk away, if that’s necessary, into the sunset with a friendly smile.