@Baby_Kina It isn't easy, but there are a few things you can do. I know you want to change, so try them and see what happens.
Reach out to people. Face your fears about opening up, and trust freely - but trust the right people.
When people reach out to you, let them. Instead of keeping them at arm's length, safe but distant, let them support and comfort you; lean on them. You'll have to watch for people trying to take advantage, but pay attention to their energy, their "vibe", and it will tell you what you need to know about them.
Recognise that it might be a slow process and you will likely always need time to yourself to reflect, but that you NEED connections with people; you MUST get out there and interact, find your tribe, the people who will naturally care about you without a second thought and whom you will care about too. These connections will take time to grow, and as they do they will thaw you out. You can nurture connections online as well, again if you find the right people to trust.
Isolation is no cure, and will only make you worse (even if there are other people physically nearby). Drop your walls, allow yourself to be accepted and loved (platonically and authentically). You've got this; you'll get there.