I understand where your boyfriend's thoughts stem from, but he's thinking in a vacuum and not in the proper social context. I am also in academia, and it is very common in my field for people to purposefully avoid dressing up. It's frequently viewed that dressing up too much means you are trying to sell your work as opposed to simply presenting the facts and letting the evidence speak for itself.

That being said, regardless of what his thoughts on suit jackets are he's not respecting your requests as his partner. Asking him to wear a suit jacket is only meant to minimize the amount of stress that you have going on in your life in an already stressful situation. This is no different from any scenario where partners ask their significant others to do something out of the ordinary in order to make their lives easier in a moment of need. If you asked him to drive the two of you to the funeral because you don't feel capable in your current state of mind, I bet he wouldn't hesitate. Instead, what he's doing now is the equivalent of debating you over whether or not you were truly capable of driving and prodding you for a logical explanation for your reasoning. Just be frank with him and tell him that you would like him to stop making the moment about himself, and simply make a small sacrifice for you because he cares about you and is open to making your life easier. If the latter two things are true, he should have no issue fulfilling your request.

I don't think this is something that's worth breaking up over, contrary to what others are saying. We all have moments of immaturity that require our partners to spell out for us.