I'd ask him what these 'excuses' are... my suspicion is that they aren't excuses at all, they're the fallout from life choices you have made that he doesn't agree with. Perhaps when you try to explain your circumstances to him it sounds like defensiveness and justification. Try being stronger with your language, something like 'I chose to study Psychology. Financially, it was a mistake. I am now trying to fix that by preparing to train for a more lucrative career. Do you have a problem with my plan? Or are you going to continue to be mad at me for choices I can't un-make that you knew about when we started dating?'

Regarding you 'contributing': You can't make a financial contribution that matches his. You can't, and aren't likely to in the future. That doesn't mean you can't be an equal partner to him, even in finances. You can do the majority of the work for budgeting your shared expenses, you can learn how loans work and be prepared to discuss them in detail for your back-to-school plans. You can bargain-hunt. You can research your household utilities and see if you're really getting the best value out of them. Basically, be proactive about your money, and let him see that you are. (Just because he has savings and is contributing to his retirement does not necessarily mean he actually knows what he's doing when it comes to money. It means he's living below his means, and is doing the first two smart things you do when you can do that. It's possible you could learn more about money than he knows, and that could be a very valuable contribution.)