I understand that this is a very difficult situation Kuri. Your relationship with your boyfriend, your history with this person and your current circumstances all complicate this.
Whatever you decide, I just hope you are very careful. I hope you will stay safe. This worries me greatly, to be honest.
While I am pleased to hear that your best friend apologised - as he absolutely should - this does not undo his past actions, many of which were abusive. This is a man who has sexually violated you (then subsequently abandoned you), neglected you and given false hope for years. My fear for you is the potential for these behaviours to escalate and put you in danger if you were to marry him. You deserved - and still deserve - significantly better than this and your current abusive dynamic with your boyfriend.
However, I respect that this is your decision and yours alone. I also appreciate the complexity of your circumstances and your reliance on others due to your conditions. I understand that you are in an impossible position, that you need the support of others to survive.
I know this isn't so simple and clear cut for you, as much as I sincerely wish it were for your sake. I wish I could take all of your pains and worries away from you, that I could keep you safe and ensure you will be secure here no matter what happens - not fearful of being deported, not ensnared in abusive relationship dynamics, not in constant, chronic pain every day, not cornered and contemplating death.
All I can do is be here for you, regardless of what you decide to do next. While I am alive, I will always be here for you and if there is ever anything more I can do for you, let me know and I will do whatever I can. Always. I care about you and want what is best for you, whatever you choose. Sending you lots of love.