I'm not to active here, but am 48 and have had the ileostomy since I was 21. I was married at the time and my wife didn't have any problem with the bag, her pants yes, but that is another forum. I have had 6 or 7 bedroom partners and never an issue with the bag.
I have been married 20 years this time, and my wife didn't have a problem at all. I approached it in different ways, with one, before we got too close, we were in the car in a parking lot and I just said, I have something to show you, pulled down the shorts and showed her, I think she was more surprised I pulled down my pants in near public than my having the bag, Others I told about it before and one I just plain forgot and she never mentioned it, with several encounters with each over the 4 years I was single.
I think the secret is your attitude about it. It really never occured to me to be nervous about it. I know that is easier said than done.
One thing I have done in many areas thruout the years, and that is a simple statement, "you aren't going to believe this", or in this case, "You may not be able to handle this but";
These phrases play on the emotion that they are going to prove you wrong, they are going to be able to handle it just to show you they can, and most will be prepared for something much worse than a bag.
I would be up front, and open and don't let them know it bothers you, it shouldn't it is part of you. One of the ladies I knew that way was a swinger and nudist, she invited me to both, I never took her up on it, not the bag, more just general feeling about it, but I asked her about it, and she said the group she was with wouldn't think anything about it.
I know it is hard to believe anyone could accept you, but they will, do not ever turn down an opportunity to date just because you are afraid of what they will think of your extra accessories.
Good luck and go have fun