[one that got away]

Since ive been with my current girlfriend and its going great but its the bedroom department im confused about. When were in bed she will tease me by passing her hand over my penis or she will tickle near my penis until she turns me on where we start kissing etc... So i will start fingering/rubbing her while shes touching me and then she tells me she wants to cum before going any further so i do this. But once she cums she tells me shes had enough and leaves me all hard & horny and kinda pissed off.

What she trying to do to me? Is she trying to have me as her little sex machine where she can turn me off and on? Its kinda pissing me off now because ive got a high sex drive and this relationship is the 1st in about 2 years as i cant keep my friend in my boxers and dont want to cheat on a girl im with.

Help?