Don't worry, you are not abnormal in wanting to scream, roil or destroy to let these emotions out. I do think there may be a better way to deal with it. I am pretty new to this, but I do think that understand why you could think that would be a way to reach out to people. My first thought would be wondering what that person's ultimate intention would be.
I would think that the first reaction of anyone that sees your wounds would be pity or even shock. After that initial novelty wears off, I think they'll try to force you into some type of therapy or to seek help. I guess, depending on what you expect to get out of showing someone your wounds, this may or may not be beneficial. I think I have some form of BPD myself but that's self-diagnosed. I'm only really now starting to pay attention to myself. I have some pretty nasty outbursts when I feel like I am unable to bottle my emotions up and I end up acting pretty crazy.
I understand the frustration of losing someone so close to you and it know definitely hurts a lot. Much like LastFlowers said, sometimes we tend to act out of instinct or we lash out because we cannot understand how to process these emotions.
I know that it probably feels that in this moment the world is crashing down around you and on this moment its very easy to get tunnel-visioned. I don't think you want this person to return to you out of some form of pity or guilt. They may really only end up leaving you again when they think you're at a stable place. I'm sorry that I cannot tell you how to deal with these emotions either.
Follow with the stages of grief to keep yourself on some sort of plan or schedule. It is almost the same as not ever being able to speak to this person again. Remember that you don't have to go through the stages in any particular order and you may even move back and forth between a few stages depending on your own situation but you will get to acceptance at some point.
If this person hasn't actually passed, one upside to keep in mind is that you may eventually be able to reach out to this person. Keep in mind that they may they not want to have you back in their life. Give them their own time to process and eventually get their life moving forward as well.
Instead of drowing myself in pain or trying to cry out for help you may not want. What I would do in your situation is to throw myself into a hobby, a task or work even. Just don't make the same mistake that I did! Don't consume yourself with distractions for the rest of your life. Take some time every now and then to check yourself.
Check in with yourself and see if you are ready to deal with it. It is ok not to be for a while. No shame in it.
Try to spend time finding some part of yourself that you can appreciate on your own and build from there. It won't immediately pop out so expect to work on this for a little bit.
I tend to feel that I need someone else to make me feel better about myself as well. So I consume myself with them until they eventually get so tired of me that they either leave me or I push them away because I'm too needy.
You can survive this. I know you will. It's not very easy right now but that's only because you're facing the problem head-on right now.
As it becomes a footnote in your history, the pain will be less and less. It won't ever go away but, it will become bearable.
It hurts a lot now and it will probably hurt you for a long time to come but keep in mind that the pain does fade away eventually. Nothing in life, neither the good or bad will last forever.