He jerks off without me

Hi ladies...so I'm in my late 20's and have only recently indulged in the wonder of men. Well 1 man...Anyway, there is a lot of new, first time experiences I am having as I have never been intimate with a man before and my boyfriend is my first.(in everything...EVERrrrything). We live together and I suspect that sometimes while I am 'asleep' he jerks off. (I have felt the bed shake and other stuff) This has happend on more than 1 occasion. Is this normal? I feel a bit inadequate or that he doesn't get enough from me so he has to give it to himself which is not a great feeling at all.