Is it a deal breaker when my boyfriend of 2yrs and 6m asks me to keep my feelings to myself?

I’m sorry you are having a difficult time in your relationship. Lapse in proper communication is a frequent hazard in relationships especially when one half is much busier with work or school. I have a boyfriend with an extremely busy schedule so I can imagine the stress you must be under.Yes, it is a deal breaker when your boyfriend tells you to keep your feelings to yourself. But from the conversation you transcribed above, I do not believe that is what he said or implied. A strong relationship is definitely founded on emotional honesty and I am happy to hear the two of you were best friends from the very beginning and have kept that friendship part of the relationship alive and healthy. Yet letting the other person know about how you are feeling is only the first step. The second step is listening to the other person and making sure they feel as comfortable as you do to talk to you about things. The two of you seem to have this down to a tee as your boyfriend told you through the chat you had about wanting to focus on his studies and that he was finding some things agitated him more easily. I expect this heightens during the weeks leading to important tests at school.I’m like you. I need to say what’s on my mind, when it is on my mind. But as my relationship with my boyfriend becomes stronger, I also realise that my boyfriend also has a lot of things on his own plate as well. It doesn’t mean I have to lie or never tell him, but it makes a huge difference to tell him at a later time when he isn’t as rushed at work/school. I expect that he can’t concentrate on your feelings when he is busy studying and that would in turn upset him also because he’s your boyfriend and I’m sure he wants to be there for you in times of need. This is more so the case when you’re not happy but sad about something. Unlike when you’re happy, when you’re sad, he needs to think about the situation seriously and wants to help you. How can he do that when he’s in the middle of studying, do you think? How about trying to talk to him after he finishes his studying? Try bringing it up after a nice meal/snack when you see each other next or during the weekend if he’s extra busy or tired. He will appreciate the effort you are making and the gesture as well.To me it seems as if he is willing to listen to you and how you’re feeling but not just at particular moments, which is understandable. This will happen more once he becomes a doctor as he’ll have many patients to take care of. Once the two of you find a pattern of communication that suits both of your needs, the more your relationship will flourish. Good luck!

It's good that you don't keep things until your bucket would run over. It's understandable that you want to share how you feel and that it's not always going to be rainbows and roses. It seems like he was asking you, but he tried to say it as if it's really not a big deal. I can understand his grade is important for him and that he stresses more when you're upset. When your significant other is upset, then it's easy to worry more and have more stress. Though, it's just how you feel. It wouldn't be fair if you'd hide how you're feeling because eventually it would all bottle up and be worse in the end. What you could try to do is that, when you know that the next day he'd have an important test, you can wait to share something that upsets you until after his test. That way you still share things, but 'spare' him extra stress when he's stressing for a test or something like that. I'm aware there isn't always a right time and of course your feelings don't come with a switch. In the end it's your decision what you want to do, but there's nothing wrong with sharing how you feel. In a relationship, it's important to be able to talk honestly.

I don't know, it seems he shared his feelings with you, about being under pressure, and asking you to reduce a bit whatever you do (not entering in detail about what does it mean sharing your feelings makes this harder to answer). Maybe you can give it a try and cut it in half? Or set a time of the week where you only talk about feelings? If it becomes something permanent and not only transitory, you'll deal with it when you know. If he's the only person you talk to about how you feel, finding more people could get him some breath.
Side note, don't talk heavy stuff by text, have a voice call instead, too much space for misunderstandings.