I think there are a number of factors involved.

Is this a hobby that spends your money, or that makes some money (or at least pays for itself)?
Do you spend more time than is necessary to care for your snakes properly? Do you spend a LOT more time?
How much time do you spend with your boyfriend?
Do you have the snakes out when you're spending time with your boyfriend?

If you are absolutely unwilling to compromise, or can't compromise, and he is unhappy with this...after 4 years...perhaps it's dawning on him that this may not be the situation he wants to be in, and you may both be better off shouldering the discomfort, and moving on.
It doesn't entirely sound as though you are in love with him...regardless of how he feels about you. Is this true? You seem more angry than heartbroken, although such things can be difficult to gauge over the internet.

You certainly will be able to find someone who is as obsessed with snakes as you are...if you did, would you be happy to spend time with your snakes, and your boyfriend, at the same time? Would you be happy if your boyfriend spent time with the snakes instead with you? Evaluate this honestly. You do need to decide what will make you happy.

It's a large world out there...too large, in MY opinion, to settle for someone who is there, instead of seeking someone who is right.