Outside perspective needed

Not sure how many demi folks are here, but this aimed towards those:

Have you ever had a partner get aroused by your meta, but the meta is not physically available to take care of your partner? How do you deal with the emotional twisting?

Not being the one that caused your partner's arousal, but they request for you to get them off. My partner says they are able to separate the experiences. IE, whether someone else turned them on, whoever they are physically with they are thinking about. Not the person who got them aroused.

I just have a difficult time not feeling like an instrument, because I didn't cause the arousal, but they want me to be the one to get them off.

I enjoy time with my partner, and getting them off. It's just an issue that has come up a few times. Especially because I feel this need to check everytime that they understand whatever we're about to do needs to be about us. This frustrates them, because they feel it is unnecessarily repetitive.

What can I do to sit better with this and feel comfortable in capitalizing on my partners arousal, even if I didn't cause it?