One of the toughest lessons I have learned in my life is that just because I love someone doesn't mean that I should be with them. One of the most essential lessons I have learned in recovery is this. Feelings are neither good or bad-they just are. I can acknowledge and respect them but that doesn't mean I have to act them out. My actions, unlike my feelings, are a choice. I would never say that love is not important but it is only one of many important factors to consider in the choice of a partner.
I do not know what you should do. I do know that today my choice is not to get into romantic relationships with alcoholics and other deeply troubled people. My experience has been that the pain of a breakup with someone I love is nothing compared to the sheer hell of riding the relapse roller coaster for years with an alcoholic who just won't or can't get it. Someone who has no trouble destroying their own lives has no problems taking everyone else's down with them. Alcoholics really only love one thing. Booze. They love it because it works to do everything they want it to do.
As both a recovering alcoholic and someone with a history of being in relationships with addicts who just don't seem to be able to 'get it' I can tell you that there were big red flags here all along. A really basic rule for a recovering alcoholic is not to get into any romantic relationships for a year! I'm sure that if his counselors in rehab knew that he was writing you love letters they would have cracked down on him and 'knocked him upside the head'! Obviously that time would have been better spent working on his written relapse prevention plan than indulging in the escape of romantic fantasy. He had absolutely no business getting into a relationship with you or anyone! Another red flag is how you describe the intensity of your love......people who are emotionally unavailable, unpredictable,unstable and chaotic tend to replace real intimacy with an intensity that can be very compelling. Paradoxically, healthy long-lasting and really loving relationships are high in intimacy but low in intensity. Even if he were to get sober and into a solid recovery it takes a good long time before someone is capable of real intimacy and relationship. Years.
Given that you are in vet school you are clearly a very bright, hard working focused and caring person. You deserve a man in your life who can share the values,world view and kinds of behaviors that got you where you are. Thing is,we don't get what we deserve in life...we get what we BELIEVE we deserve. So I ask you.....is this all you believe you deserve in terms of a loving, available,stable partner?