I'm going to agree with what the other ladies have said so far. Be honest.
Also, if it were me that you were with, I'd prefer that if you've reached the point of no return, don't tuck tail and run to the bathroom. Ride it out and enjoy the orgasm, don't make a show of it, but enjoy it. I have been with someone that, while they didn't have a PE issue, they had the issue of staying hard once in the condom. But he made it a point to make sure I had a really good time, even if he couldn't do it with his cock. I didn't ignore him the entire time either. We just enjoyed each other's bodies and still had a good time.
I'd also consider not holding back on masturbation just for the bigger boom, at least when you're going to be with someone for the first (or second or third) times. I would be a LOT more forgiving of a guy that has a PE if I know that it's not a usual thing for him from previous experience. I know nerves are still going to going to come into the picture, but I wouldn't expect saving up for a big night to help the staying power.