Hello
I don't see any mental issue, but a bit of miscommunication here.

I think perhaps you may have jumped to conclusions a little bit. You assumed that his not giving you money meant you were not important, but this is not the only explanation. It could be that you've been together for a long time and he thought it would be ok this time to leave it a while - that you would understand. That is, in fact, him taking you for granted, but that's very common in a long-term relationship. You are well within your rights to say that you feel a bit taken for granted, but it's the way you say it. I don't think you acted crazy at all, but your note may have been more effective if you had said although you know he loves you, sometimes you feel a bit taken for granted - better still, it would have been much more effective to explain right when you felt it that you felt hurt he had not offered to pay you and ask to talk about it calmly. But again, feeling uncomfortable with confrontation is pretty normal and not a 'mental issue'. It's just maybe something you could improve upon.

As for your boyfriend's overreaction. To me it sounds like he was already feeling really bad about the money thing and it was already on his mind. He jumped to his defense as if he had been expecting to be attacked. He then suggested in his note that you might want him to leave, as if he's expecting that he has let you down so hard that you wouldn't want him anymore.

Basically, I think you've both been having arguments in your own minds for a while and those imaginary arguments just bumped into each other. You've been thinking he doesn't care about you, and he's been thinking he's failed you. You've both been trying to read each other's minds but your thoughts have been coloured by your own perceptions of yourselves.

Sit down and have a calm chat. Start by telling him you love him and you would never have wanted him to leave. Admit your own flaws first - tell him you think you didn't do a good job this time in communicating an issue that was upsetting you, but that you will make sure to do better in your communication in the future. Then tell him that you want to hear his point of view and you want to understand how he has been feeling because you have picked up on something in his note that suggests maybe he has been feeling bad recently about the money situation. Have an open discussion, is what I'm saying, where you are curious and interested in each other's worries and happy to communicate openly and calmly.