Lack of sympathy toward others : addict symptom ?

Hi. Your boyfriend doesn't seem to intentionally be doing this. Could I start off by suggesting you talk to him about it when you are completely healthy and have put aside all nerves so that you two can really work on it. If not, I really don't think you are obligated to someone who doesn't seem to care. We all need some support and nurturance when we are with someone, and not having that can result in worse issues down the road.
But MOST importantly, his attitude and behaviors in distressing situations are not healthy. They are clearly interfering with your relationship, and it is dangerous that seeing someone in pain causes him to barely bat an eyelash -- this is bad. One should be alarmed when someone is in pain, especially a girlfriend/spouse. When we see someone do something, or witness a person feel emotion or pain or pleasure, our mirror neurons will tell us how to feel or how it would feel if it were happening to us. This doesn't seem to be the case with him -- he seems to be lacking the ability to comprehend pain, the degree to which it is affecting the person (maybe his past drug habits have built his tolerance or repeated exposure to these morbid experiences has caused a numbing in his perception of these things). His lack of empathy/sympathy could be a result of a personality disorder, which would most likely be due to prolonged drug abuse. If done long enough, irreparable damage to brain can be incurred and permanent personality changes can occur, because learned experiences are 50% of what shapes us. Knowing what your significant other has been exposed to in the past is not judgmental, but also a cue to judge a person on reasonable grounds -- we're human, we are conditioned to judge for our own survival. Personality disorders don't occur alone, they are usually accompanied by many other eroding personality traits that result in an overall disruptive personality that can affect many areas of our lives. Everyone has these tendencies, such as schizoid, narcissistic, paranoid, etc...and everyone can meet the criteria and think they have a disorder but at the end of the day -- when it disrupts daily life like this, there is clearly an issue. I hope this at least helped you a little bit. I am studying personality psychology, this is everything I know applied to what I have heard so far of your situation. Make the right decision for yourself, and if you do try to help him, make sure he is ready to help himself first! Best of luck to you and your health..
- s.