Thank you for bringing your question to Just Answer!
You don't have much choice about giving him space, as he's broken off the relationship. He's made a choice that drinking and drugs are more important to him than being in a relationship.
He's old enough to realize the consequences of such a decision, but is choosing to make it anyway.
Usually when people go down this path, the only thing that will turn them around is consequences. Trying to save or protect him from getting hurt is not in his best interest, because 1) you can't save someone who doesn't want to be saved. 2) if there aren't any consequences of what he's doing, there's no reason to stop.
You note that, at 19, he was "aways a smoker/drinker", which says he started using substances at a pretty young age. You may be seeing the progression toward addiction/alcoholism. Choosing substances over another human being is a pretty big red flag.
Trying to control him or his behavior won't work. If he becomes apathetic toward your relationship, that tells you it has run its course. Very few teenage relationships make it into adulthood. It's impossible to predict how long it will be before he chooses people over substances--and if he has a predisposition toward addiction, it may be many years. Based on the normal psychology of men, it would be unlikely for him to return to a past relationship--unless it seems like a challenge. Men like competition and challenges: that's why being too accommodating doesn't work with them. It may seem counter-intuitive, but your best shot at getting him to miss you is for you NOT to miss him. Read Temptations of the Single Girl and/or Why Men Love Bitches: From Doormat to Dream girl http://www.amazon.com/Why-Men-Love-Bitches-Relationship/dp/1580627560/ref=sr_1_1?s=books&ie=UTF8&qid=1322762333&sr=1-1
The only productive thing you can do at this point is work on detaching from him. It would be great for you to read Melody Beattie's books on co-dependence to help you through this time. Here's a link: http://www.amazon.com/New-Codependency-Guidance-Todays-Generation/dp/1439102147/ref=sr_1_5? s=books&ie=UTF8&qid=1322762430&sr=1-5
Re-building your life without him will either make him realize how much he misses you or it will get you started on a new path that isn't dependent on someone who has treated you this way.
I have been concerned myself that this may lead to an addiction, but he's been abusing drugs since middle-school and he absolutely refuses he has a problem.
Are you saying he has to hit rock bottom or be faced with some kind of consequence for his drug/alcohol usage before he'll lay off it?
I have made it my goal now to try and leave him alone, he was always one to be crazy and clingy to me before all this, and not calling/texting/etc just might make him think of what he's doing. He has no real life outside of the drugs and me, and I was wondering will this lead to further addiction?
He has no real life because of the addiction. It sounds like he was even using you as a sort of addiction by being crazy clingy. Yes, hitting bottom is what gets most people to stop. You can hear the stories from the addicts/alcoholics themselves here: http://xa-speakers.org/pafiledb.php You'll hear first hand how they rejected all offers of help, and denied having a problem.
If this started back in middle school, there is virtually no question that he's in or close to addiction.When substance use interferes and causes problems in the rest of your life, that's an addiction.
Your decision to back off is the right one, but you're going to need to educate yourself about alcoholism and addiction--when a person is as helpful and concerned as you, they tend to attract people with addictions (because they know they'll be taken care of and won't have to be responsible. ) Go to the Alanon site--which is for people who have alcoholics in their lives: http://www.al-anon.alateen.org/is-alanon-for-you You want to make sure that attracting addictive people into your life doesn't become a pattern.
Well thank you for the advice, my father was a heroin addict himself and my mother was addicted to gambling, and I do feel I have been attracted to him subconsciously because I have been around addicts all my life.
I'm going to keep hope that he gets better but I know constantly trying to make-up our relationship and constantly trying to tell him he has a problem won't help anything, so I'll give him time to live this way and maybe in a state of being sober will realize what's going on.