Is it me or a symptom of ADHD?

Let me start out by saying that I consider myself extremely lucky to have an ADHD partner who manages his ADHD freakishly well and that we are in a very long long distance relationship which cannot end for another year or so due to previously made and important commitments. Despite this we have a spectacular relationship, which like any relationship has had it's ups and major downs, but unlike any other relationship that I've ever been in I've never questioned that he is my happily ever after. I know, without a doubt, that we are meant to be together. I know that within his heart he feels this way too but we are not engaged. I have been waiting for/expected it for almost two years now and I have been honest (but not at all pushy) about my feelings on the subject. It wasn't until around 7 months ago that I finally learned why he had not asked yet: he was unsure. I was heartbroken! To hear that the love of your life is unsure if you are good enough to be his happily ever after is a very scary experience. In hindsight I understand. It wasn't until he found this website that I was finally able to understand how ADHD affects us as a couple and accept/learn that it is a part of our life, not just a problem that he has to deal with.

Now I am left waiting to see if this change is finally enough to make me 'good enough'. Our last conversation about marriage highlighted a problem and thankfully it was via IM so I can share it with you:

"i mean, think of it like this, my brain is a freeway with like 10 lanes of traffic going 100 miles an hour and then the thought of proposing is like a semi swerving wildly out of control across the traffic, with like three trailers attached"

He is going to school and can't afford the distraction of having a "semi swerving wildly out of control across the traffic, with like three trailers attached" but being engaged is REALLY important to me - not planing the wedding or actually getting married before he finishes school but just making that promise to each other.

Like any happy ADHD couple we each make a serious effort to communicate effectively with each other and we each make a lot of  compromises to ensure both people are being supported and getting what they need out of this relationship but waiting another one and a half to two years for my partner to propose is not a compromise that I can make. Nor can I ask him (any more than I already have) to ask sooner. I do understand why proposing wouldn't be the best thing in his life right now but I'm afraid that our relationship wont make it until he's ready.

I really need some advice please!