I wouldn't consider his treatment of you to be standard for how secondaries get treated. This is how he is treating you and it isn't working for you. Whether you were a primary, secondary, tertiary or his only - no label one could attach should be reason to accept treatment that makes you feel mistreated.
This is also why you shouldn't try to figure out (rather than asking outright) why he is treating you this way such as he must be seeing other people. People either treat you how you state you want to be treated or they don't. If he were seeing other people, would it make the way he is behaving towards you okay? If not, I wouldn't bother offering up guesses that you feel will make you sound jealous or desperate. Simply tell him you liked it when he did treated you the way he previously did and don't like how he is treating you now. Anything else sounds a little bit like you're offering up justifications for the way you're being treated and that would only work if there was something going on that would make all this acceptable to you.