We have all lost friends, for many different reasons. Sometimes we move away, other times you simply just don't get along anymore. Whatever the case may be, it is okay, and remember everything happens for a reason.
It always sucks when you have a falling out with a close friend. So many emotions and thoughts play into it, like "Where did I go wrong," "Why are they doing this to me," and worst of all, the feeling of guilt. You may want to fix and mend the broken parts of the relationship, but it may be best to just leave it alone for your own sanity.
It is okay to try and reach out a time or two, but it is probably best to leave it be if you are not receiving a response back.
If the other person is not responding, it is clear they do not want to make amends or are not ready to make amends, especially if you have attempted reaching out more than once.
It sucks even more when the person you fell off with has mutual friends with you. It is hard to totally erase the hurt when your friends are hanging out with the person who hurt you. Please remember, you cannot control the opinions your friends have of that person, and you cannot force them to not be friends with them either. That is unfair of you and in situations like these, you should always be the bigger person.
Another reason this situation may make you feel so terrible is that this person probably knows a lot about you. You probably spent a ton of time getting to know each other. However, if this person is not reaching out to you to make amends after you've tried reaching out, they probably do not care enough to spread your business around town. Whatever happened to cause this falling out has clearly allowed them to move on and with that, they most likely aren't going to want to spend any extra energy on you.
This may feel like the end of the world, but it is not.
You still have other friends and your family. You have the activities you have always loved before you were even friends with that person. And if you are taking initiative to be the bigger person, you have the peace of mind knowing that you tried to make things better with that person.
You are not a terrible person at all.
Not to be harsh, but it is time to wipe away the tears and stop the pity parties. If you had an intense falling out with a friend, it probably happened for a good reason, as I said before: everything happens for a reason. It is always best to be the bigger person in the situation and sometimes things may work out between you two.
But, remember your life never revolved around this one person. You have other endeavors to focus on. It is possible to move on. I know that sometimes losing a friend, especially if they were a best friend, can hurt worse than a breakup, but you are strong and time heals all.