First and foremost, the absolutely priority here is your education. You can certainly balance the two and I'm not saying that you cannot be in a relationship and do well in your exams, but if there are things that are causing you stress and anxiety (such as having to lie to your parents to spend time with your boyfriend), it is important to minimise that during your exams.
This is all a very typical high school/sixth form relationship situation, both as regards your relationship and everything being intertwined with your friends and his friends. Nothing unusual about it at all. Fortunately it seems to me like you've been very mature about this so far, and have been very clear with him in communicating both that your exams take priority, and what that means, or may mean, for your relationship. To my mind the better option is probably to continue with the relationship but be realistic about the amount that you'll be communicating with and seeing each other during mocks and exams. It may be that you can meet up here and there during those periods, but you both hopefully appreciate how important those are, so in reality the relationship will take a back seat for you to focus on them. If he acknowledges that too, I don't see why you can't continue with the relationship but tone things down during mocks and exams.
It all depends on the specifics though. If the temptation of the relationship is too much and you need to be more formal about it, by all means go on a break to draw a line under it. If he can't respect those boundaries or the break doesn't work, break up with him entirely. You can always rekindle things after exams regardless of what you do now. But given that you're both enjoying this relationship and want it to continue, I don't immediately see why you'd break up entirely, or even go on a definitive break, when you can just acknowledge that your mocks and exams will have to take priority at certain times.