You are making me dig back in my brain to figure this out but it's good because I am curious as to my own answer! =)
I have had 4 relationships during my crohn's tenure. Tenure lol.
Guy #1 - I really don't remember when I told him or how it came up but I know I looked good and was doing really well when we started dating. It was shortly after we started that I got diagnosed with Crohn's and things rapidly took a turn for the worse health wise. I started high dose prednisone, got a fat face, ate everything in sight and had acne from the medicine. He loved me and wasn't going to let this be an issue, I never once heard him complain or judge me for it. The only affect the disease had on my relationship was in the bedroom. When I had a lot of diarrhea and blood he was less than eager to get intimate. I totally understand this and can't blame him for being disgusted by that. I truly don't think IBD had to do with our breakup but it may have been an additional factor for him when considering it. It was a mutual break up.
Guy #2 - I was doing OK during this time period and this guy was really sweet and didn't care at all. I think I told him about my crohn's on the first date because he was just so adorable and understanding and it was a total non-issue in any way.
Guy #3 - This was my boyfriend who also had IBS, I have mentioned him in other threads. I told him on the 3rd date and he was pretty relieved because he said he needed to be careful with what he ate too. Since we both had stomach pains, we were totally understanding and cooperated with one another when we didn't feel well enough to go out. It was a truly great relationship and he was very accommodating, often picking me up from work and going out of his way to make it easier for me day by day.
Guy #4 - This guy was AMAZING! What a sweetheart this person was and is. I told him on our second date. Total non-issue at all. I was very concerned that my scars from surgery would contribute to an ick factor especially since they were relatively new at that time. He said "these are badges of honor and show you persevered through a hard time" and proceeded to kiss them. How sweet? I was also really struggling with severe allergic reaction to Humira at the time and he was totally understanding going above and beyond to help me in any way he could. He is honestly an amazing guy but sadly I did not feel the chemistry and ended the relationship but remain close friends with him.
Looking back at my relationships it seems most were really good about understanding my crohn's. I have had some bad experiences with dating but anything with anyone more serious turned out to be OK. This still doesn't eliminate that fear that it will be hard to find the next good guy out there and the trouble with telling people about this disease.