Sending a love letter saying sorry is one of the most beautiful things you can do. No, there is no guarantee that your apology will be accepted, but a love letter saying sorry will always be in the persons memory for many years to come. Why people don't think they don't owe anyone an apology is beyond me. How does someone, knowingly hurt someone, and not say I'm sorry?
Make sure when you write your letter you are very sincere and the letter is heart felt. Saying your sorry describes who you are as a person. Even if what you did is so very wrong, you need to say you are sorry.
Sending a letter acknowledges that you hurt someone else, you recognize it, and apologize. In matters of the heart, your letter may not ever be enough, but it's the thought that counts. And just because you say your sorry, doesn't mean that everything is going to be ok now. But do it anyway.
Send the love letter saying your sorry that you never did. So what time has passed. Sometimes it takes years to get over a circumstance, or to gain maturity so then you can reflect on what you did.
A letter can only make things better. You need to understand that you have hurt someone deeply. You have literally wounded them. And yes, they will recover, over time. But in the mean time, this person is hurting bad. Every day, and every minute of the day. And you are sending a love letter saying sorry because you are, or were, in love. And if you are in love as much as you say, then the absolute worse thing you could ever do is to hurt the one you love
Love is precious, and if you are in a situation where an argument pursued, a misunderstanding, and some things were said in the heat of anger, you need to learn how to disagree respectfully. You both are individuals and look at things differently, and that's ok. But if you love this person, don't say things that you know is going to hurt them, or push their buttons.
And if you are in a position of unrequited love, (love not returned) then sending a love letter needs to be written, from both of you to each other. One of you needs to say your sorry for using you and telling you that they loved you, when they really weren't in love with you. The other needs to send a letter saying sorry for not letting go and keep trying to make things work.
Many say they don't know what to say or how to say it. Just say what is in your heart, and that will be just fine.
Does the letter saying sorry make things all right then? Not necessarily. If you are recently separated from each other, you two still may be able to work things out.
If this is a letter saying sorry from a relationship that has ended, there is generally no chance of going back, but send the letter out of the respect and love you once had for that person.