I'm wondering how you're equating his being in detox to his not loving you? or leaving you? The main reason why an addict will leave their partners is because the partners enabled them using and would do so again. But you've been with him 4 months, and his addiction started i'm guessing years ago.
One thing, if he is getting help with an Addictions Therapist, and he get's to talking about you being really needy it might be suggested that he needs to look after himself, rather than to have to fixate on making you feel better. This time has got to be about him getting help for his addiction , it's a life and death struggle, and if you cannot support him by allowing him all the time it takes (months in rehab or whatever) then you're not the best type of partner.
My advice to you is to ask him if he can go to residential rehab (more nights away from 30 to 90 days away from home). He might also be offered Outpatient rehab, which is usually 3 nights a week, and meetings in NA every night. You cannot be a high maintenance gf if you hope to help this man. You can go to "open" meetings of aa or na with him but his getting clean and sober will require him to comfortably leave his home after work (assuming he works) to go to AA or NA meetings.
So if you are needing a lot of his time to make you feel safe in the relationship right now, that would work against his recovery. You may need to get a hobby or go to Alanon, (a family group of addicts) or Naranon (a family group for drug addicts) that teaches families to live with their addict without enabling them.)
You see? You have to be strong in your love and be supportive for him, or you need to break up with him.
I think if you tell him that you want to fully support his recovery, be part of the family group, willingly support his going to rehab, and helping him to stay sober, (not drinking in front of him, having no drama or adding drama to his life) etc. he will probably feel that you and he will be able to overcome this relapse and have long term sobriety. If you appear needy, he might choose his therapy over you.
So.. don't be needy. Shut that down and don't let it out of to see the light of day. Do what it takes, by learning how to support an addict, and you'll be in your best advantage to get what you want. ( a relationship that lasts.).
Did something happen before the relapse? was there a fight or anything that went wrong.?
Was he gong to any AA or NA meetings when you met him? IF not, that's a problem. Most addicts in early recovery need mutual support groups. (however some can stay clean without them)
When you say "we got him into detox" who is the "we" does his parent's know of his addiction (i hope so ) Is he close to his parents.? does he have them for support?
You haven't said that you were aware of his addiction. Were you?
No judgement here. Just realize you cannot control his addiction, or what he does when he gets out.
If he thinks he is "too good for you" when he gets out - there is very little you can do to convince him otherwise.
I encourage you to read co-dependent no more - great read! Take care of yourself:)
I am divorcing my unemployed husband of 12 years, who I put trough rehabs 4 times (I could have paid off my mortgage by now), who put me and my son through hell. I have being gainfully employed and fully supported him through the years. He ended up cheating on me with addicted unemployed woman of his age (I am 14 years his junior).
IMO - it's not worth it. You are just dating him for 4 months - let go.
I'm worried we haven't heard from you. How are things? Can you talk about it?