I've never seen any statistics, but a chronic health problem surely does put extra stress on a relationship. Some folks have no idea what "in sickness and in health" really means. My marriage broke up, in part, because of my illness. My ex tried in his own way, but he really didn't have it in him to be truly supportive. He was at the racetrack when I had to be rushed to the ER when I was first diagnosed. He claimed he wasn't a "nursemaid." My family was livid when they saw how sick I was and the state the house was in after I'd been bedfast for a couple of weeks.
Thank heavens I've since remarried a wonderful, caring and supportive guy. I was in remission when we were dating and first married, but since I've had a mild flare lately, I couldn't ask for a more considerate and helpful partner. I'd advise anyone who's not already in a long-term, committed relationship to be very careful about their choice of partners and very open and honest about the possibilities of UC flares on the front end.