Submitting to something that you don't enjoy in order to please someone else can be tremendously powerful. It's a valid experience and not "less" than masochistically reveling in pain. Probably you can't go as far with the pain as a real pain slut but I don't think that should worry you. If your partner wanted a pain slut he'd find one; if he's playing with you, then he probably values your submission as much as you enjoy giving it, and then the pain is a means to an end, not the end in itself.

In terms of how far you can go - only you can discover that. It might be further than you think.