What it probably means is that he is self-harming. Some researchers think that some individuals who self harm dissociate from the pain by getting fascinated by the sight of their blood when they cut. For others, it may be confirmation that they have hurt themselves. There are a number of proposed names for the behavior — and there are a number of diagnoses associated with it. Without knowing more about him, I can’t give you more specific information.
What I can say is that your boyfriend is in great distress. He apparently trusts you enough to share the extent of his problems with you. I hope you will urge him to get some professional help. A person in this amount of pain needs more support than you can give him. If he won’t talk to a counselor or his parents, I hope you will tell him that you need to do so — even if it means that he won’t speak to you again. Ideally, he should be involved in the decision about who to tell but if he can’t or won’t, go to a teacher or school counselor you trust and enlist their support. Loving him means doing your best to get people involved who can get him the help he needs.
I also urge you to take care of yourself by going slow with this relationship. I’m sure he has some wonderful qualities or you wouldn’t love him. But he may be in such distress that he won’t be able to return your love in the way you want and deserve. Another possibility is that he may become dependent on you to “save” him by being the only person he can talk to. You can’t let that happen. As much as you might like to be the one who can relieve his pain, you don’t have the skills to do it. He needs more help than even the most loving and best intended partner can give.
I wish you both well.