There will be many people who come into your life for all the wrong reasons, and they will destroy you if you're not wise enough to know that they shouldn't be part of your existence anyway. It's all up to you to recognize these toxic people and not allow them to make you feel any less than what you are, and what you deserve. They will try to belittle you, your dreams and your goals because they are insecure and unsure with the person they are themselves. They will not motivate you or encourage you to be the best you can be because they are actually secretly hoping for your downfall all the while. They will do you wrong, then deny the fact that they did such a thing, and will even justify it to no end because they will never be able to admit when they're wrong. To them, it must always be your fault and if you're not strong enough, they can even make you believe it too.
Your life begins the moment you come up with an answer to these two questions; what kind of life do I want to live and who do I want to be? If you aspire to live a successful life full of joy and happiness, then you need stop allowing this kind of negativity from these kinds of people, into your life. They have no business tearing you down. They have no business interfering with your plan, your goals- cut them off. Love yourself enough to let them go; realize your self-worth and how you don't deserve what they are giving you. You will feel as if you lost eighty pounds of dead weight after you have, and you'll feel capable of doing anything you put your mind to.
Who do you want to be? If you want to be a good person who has not become bitter over the fact that someone has made you such, cut that person off. If you want to live happily and successfully, you need to let this person go willfully or such a thing will not be possible. It will be an uphill battle and they will do nothing, but drag you down to the level they feel they're stuck at. You'll never grow, you'll never accomplish all that you want to all because they say so. You'll feel horrible about yourself all because you might be afraid to lose that person, but why? It doesn't matter how long you've known them. They have done nothing to show you that they're afraid of losing you. You simply have to consider yourself, and being selfish in this situation is a good thing; a great thing.
And you don't have to explain yourself. You don't have to explain why you don't want to be involved with them anymore and why you don't want them in your life because odds are, they already know. They just refuse to admit they were wrong and refuse to apologize, but that's okay because now you know they were never meant to be apart of your life anyway, that they never deserved to be there in the first place.