Think of the problem as a business and technical challenge. That's what it is. It is not your personal character deficiency.
There is nothing wrong with listening for a few moments then saying "please let me restate what you just said. That way we'll both know I understood." You can also say "wait, help me understand what you just said." The trick is to ask for his help.
You're an architect by title. The heart of an architect's job is making clear and simple plans for builders to follow. It's well known in IT that clear plans help lead to good systems. So don't stop striving for clarity and simplicity.
Think about why you can't keep up with your colleague. Is it because
- you need to learn more about a specific area of your job?
- you don't know some parts of your company's set of tools?
- you don't know the company's internal jargon yet?
- he talks too fast?
- his thoughts aren't clear?
The first two of those reasons are your responsibility to fix. Time to hit the books. Tell him you are scrambling to come up to speed on those topics.
The rest of the reasons are your joint responsibility to fix. System design is hard work. Most of that work involves converting murky ideas into clear ones. If his thinking isn't clear, don't hold it against him too much. Part of your job is to take his murky ideas and make them clear.
I suggest you have a conversation with him about his frustration with you. "I can see you're frustrated that I sometimes don't follow what you say. I'm working hard to learn this job and learn to understand you better. Do you have any suggestions about helping me come up to speed more effectively?" You're gently reminding him that part of his job is to make you successful.
Keep this in mind: it's no fault of yours you have things to learn. We all have things to learn, no matter our level of experience or time in job.