Hey Jj123. Don't forget, the pain of resisting to lust if much less than the pain of falling.
I've listened to a shiour where the Rav said that our be'hira is not on the act itself, but on the vision of the situation what we set up before the act. Indeed, before we fall, we create a false vision of the situation in which the avera seems justified, it might even seem like a mitsva ! This is where the y'h acts : falsify the truth vision of the world.
Once you have accepted a false vision of the world, doing the avera is just a consequence of that acceptation.
So this is where be'hira stands : do I want to listen to what is true, or close my eyes on it so that I can succomb to lust ? Do I listen to the y'h right away or do I take a few minutes to think about it ?
We know that if we wait a little bit and meditate on simple truths with our reason, the y'h has no chance, and this is why sometimes we intentionnally close our eyes on these truths and act quickly before we have the time to think.
So maybe you could just take the time to think about some simple truths you already know about this fight, and medidate on it with your reason ?
For example : Give in to lust 1 000 times will never be enough, and give in once is already too much. If you fall, the lust will come back anyway, and stronger, making the challenge even harder.
The y'h makes you think that if you try to resist, the urge will stay forever, so you'd better just give in right now, it's his best trick ! If you say "no !" just a few times, then the urge will fade away (it will come back later, but you'll be safe for a moment, and the next time you'll be stronger and the urge weaker)
This is the truth.
Focus on how you will feel after if you fall, and how you will feel if you resist. Tell your y'h "Your offer is interesting, but look, this is how I will feel after doing what you want me to do"
Keep moving forward !