It's upsetting to know you are going through this. But from how I understand your post, you are aware of certain missteps on your part. And that seems like a good thing- you know what you need to correct. It would be difficult, of course, but you know where you need to start :)
Also, you may have made a "terrible mistake", but that does not make you a "terrible person". Our mind messes up that distinction but it is an important one!
When we spend time alone, we tend to go into retrospect about our deeds, and sometimes we get too harsh on ourselves as well. Remember we are human and mistake are natural to occur, and sometimes we see our deeds as if committed a sin, but one cannot punish oneself for our past sins. People who love you when they see a change in your behaviour, thats the only apology they are seeking. You made mistake, you can correct it, if nothing express your heartfelt apology, and never go back to the behaviour trend you used to engage in. Thats one way to kill the "lost feeling".
2. Do this with only an intention to reach out and let the other person know you truly take responsibility of your actions, but don't expect anticipation, cause we don't know how much time the other person needs to accept this and reciprocate.
3. To own up to your actions, and starting as a clean slate needs courage, you reached out here so you have given your self a head start already!!!
4. You don't have to go all out, in one go, so it bit by bit. Be it a text or call, but don't forget to acknowledge yourself. It's you who is taking action, when intention is clear that exactly what is communicated.
5. Breathe. Breathe. Breathe. You are worthy, you made mistake you are rectifying them, even when people don't respond don't take it to your heart, caus dhere the intention is to let the loved know you love them, you are sorry and you are willing to put nothing but the best version of yourself forward everytime.
6.structure your day for yourself as well, please do take care of your meals, spending some time in the sun, doing some cardio at home. And remember you are not in it alone. You never were, cause your love for yourself is enough, and everythinf else is just an add on.
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Acknowledging our mistakes is the first step to change. Take this chance to reflect on what you want your life to be like, who you want in your life and what you can do to make those relationships better. But first, learn to forgive yourself. Those who love you will see the changes you've made and they may find their way back to you.