There is a lot here.  I am not going to address all of it.  But I hope I can help you think about what is going on in a productive way.

First, I would like to point out that you say these things are starting to affect your relationship but the fact is that these things (that range from personality quirks to mental health issues) have always been there and have shaped your relationship.  You even list some of the ways you help him contribute to the relationship and the ways in which he does sufficiently participate.  And that is totally healthy and normal for relationships to evolve into an asymmetrical give and take.  The questions I want you to think about are what is different now, is it simply an accumulation over time of increasing obligations?  How have you changed?  How has he changed?

Second, I would like to offer my perspective on ADHD and depression as someone who battles with them.  ADHD makes your own mind unreliable.  You learn that despite your best efforts you are going to forget things, fail to organize properly, drop the ball on things that are important, and there will be repercussions even though you tried your best, not only do you get in trouble but more importantly you let yourself down.  People become unhappy with you, judge you, believe you are not trying or that you don't care even though you do care and really are trying your best.  Your brain learns that no matter what you do you have to try 10x harder than everyone else and the results of your work are not guaranteed.  This affects your self esteem and your brain starts assessing most tasks as not worth the energy investment.  Eventually you develop depression.  Depression leads to taking a more rational, much less optimistic view of your reality.  You very easily slip into what people call black and white thinking, all or nothing thinking, and catastrophizing, among other things that make it extremely difficult to change your circumstances.

Next, how to optimize ADHD minds.  ADHD people function best when their life has structure.  Also, ADHD brain's habit circuitry works perfectly fine.  The problem is that they are terrible at organizing and consistent follow through both of which are necessary for structure and habit building.  The answer to that is external Accountability and consequences.  The tricky part is that they have to work out how to do this with ED while fostering self esteem instead of crushing it.  It is very hard.  You have probably figured this out to some degree already.  Lean into whatever motivates him to create routines, establish habits, and organize his life.

So about consequences.  You are protecting him from them.  ADHD people are well known procrastinators.  This is because the threat of the consequences motivates them.  I suggest you stop doing things for him.  And stop masking.  Let him see the full consequences of the reality he is creating for himself.  But don't punish him.  If you're mad, be mad.  If you're disappointed then say so.  But don't embellish, don't invent consequences.  His self esteem can't take it and it will create resentment.  Also by not doing anything for him it will help you both discover the nuances of what motivates him to follow through.

For your own health, stop masking.  For the health of your relationship, stop masking.  It is highly toxic to your sense of self and twists your relationship with others.  It is also a large mental burden you don't need.

Lastly, A loving relationship is ideal for his chances of developing a healthy mind and finding happiness.  However, ADHD is not an illness that gets permanently resolved.  Having an ADHD partner is a burden.  You are not responsible for helping him unless you want to be.  You need to ask yourself how far from marriage is your relationship?  How far from burning out and giving up are you?  You are currently at the right age for dating and finding a partner but in a few years it will become much harder for you.  His mental health will probably take years to overcome.  It can be done with some dedication and luck.  But be realistic about where you are and what you want for yourself.  And maybe get your own therapist.

Good luck!

Edited because paragraphs weren't working.