Does Medication for ADHD really make that much of a difference?

My Husband was diagnosed just a few weeks ago with ADHD (the combined type) and he is 33 years old. It seems very severe. In fact, the doctor told us that it wasn't even questionable whether or not he has ADHD since he scored a 105 out of a possible 120 based on the questions he answered. We're looking into him getting on medication, but it seems to be taking awhile for us to get a doctor's appointment especially cuz we had to find one that was affordable enough for us. I am also really concerned about the costs of the medication. I understand that he will have to be on medication for the rest of his life really. I'm not sure I'm going to be able to accept that. I feel increasingly frustrated with him though and as it is I feel like I can't even talk to him anymore because I feel so disrespected. I feel like nothing I say even matters to him anymore. I think about leaving him on a daily basis, but yet it still makes me very sad/depressed to imagine a life without him in it. I don't know what I should do. How do you tell if you need to leave or when you've reached your breaking point really? We have been together almost 4 years and married for 2 1/2 years so far, yet it feels like we have been together so much longer. I feel like he's no longer the man that I married, but he insists he's the same person. I just don't see that because he's always negative, blaming me, ignoring me, getting distracted, not being productive around the house, or forgetting something that I have told him. I have told him several times what he needs to do and I send him articles and we bought books for him to read. However, I'm not noticing any improvement or that he's even trying to do better. Should I wait to see how he does on medication? Can it make that much of a difference right away as soon as he starts taking it? I am not a very patient person so I don't think I can wait around much longer since I am so depressed and angry/frustrated everyday. This is not healthy for me at all. It doesn't help that we don't have nearly enough time apart. I wonder if a trial separation will help us? I feel so lost and alone right now. I have no support from any friends or family and I don't really talk to anyone else because of that. We are seeing a therapist, but I don't think we will be able to afford to continue seeing one for much longer. Plus, It doesn't seem like our therapist really understands ADHD that much. She did at least advise us to look into getting him diagnosed because she picked up on the symptoms. We are currently reading The ADHD Effect on Marriage since our therapist recommended it to us, but it just frustrates me so much because It seems like it's saying that I have to do more work than my Husband. I don't want to do that and I don't have the energy to do that. I already feel overwhelmed. I didn't ask to marry someone with ADHD and I don't feel like I can ever accept his ADHD. I feel more so like I just need to leave him, but I still feel like I care for him a lot. I'm unsure whether or not I love him anymore because his severe ADHD has just made him so difficult to live with.