You have every reason and right to feel the ways that you do. I am sorry it is an uncomfortable situation. If he isn't interested in her, but in you, you didn't purposely create that. Don't allow that to become a problem that stands in the way of what could be something good and enjoyable. I agree it should be kept discreet for now, and I admire you and him not wanting to hurt her. But there will come a time when, if it is meant to be, all will work out and you won't have to be concerned about her anymore ~ as you shouldn't have to. In the meantime, make it all that you are able and it will work itself into place. There is common courtesy, but you have feelings too and you cannot always protect another person at your expense.