Cat,

I wouldn't say lie.
Probably acting in a way you are able to at least tell her an half-truth. If she asks. Without her asking I wouldn't even tell her anything at all.

I think we can agree with each other upon telling her a half-truth (or a truth which holds true for a part of the time of the intercourse) is better than having the head full of desires.

And there is alwáys a middle way, like, in this case probably:
Starting with thinking about a certain boy, and if aurousment reaches a certain stage, think about the love you feel for her, shifting to your love for her..

Not to your sexual feelings (which seem to be close to non-existant) for her but for your love to her, using the higher states of your arousment as something like a ski-jump.

So you wouldn't even have to lie (and breach a commandement), in some moments of the intercourse you would have thought on her and not on the boy.

Sometimes small steps are easier to bear.
Not that black-and-white of thinking about the boy with the result of having to lie or fighting yourself through an intercourse which makes you feel sick.


Worth giving it a try?
I don't know.

Greetings,
Sushil.