Donna and Thorne were briefly engaged, but never married.
Donna's been married to Eric, was engaged to Thorne, dated Ridge, was involved with Nick, and I think she and Bill just kissed the one time?
Katie's had a crush on Eric, is married to Thorne, was engaged to Ridge, was engaged to Nick, and was married to Bill twice.
Brooke's been married to Eric twice, was married to Thorne, has been married to Ridge several times, was married to Nick, and was married to Bill.