I'm not sure if it should be spoilered or not, time-frame wise, but - skip that. Let's say Obi-Wan did have a relationship in the past - assume as you will it was Siri (from JA), Satine (from TCW) or an OC - I'm not entirely sure it would be entirely fair to categorize such as "secret." IF it had been a physical relationship, it wasn't openly spoken about, but that does not make it secret. Few people go around announcing, "By the way, I'm intimate with so and so - thought you should know." Not speaking about something is not necessarily hiding it. There has been "talk" (boards, various places) that had Anakin and Padme merely been "good buddies" without the marriage (and Anakin's possessive obsession with "his" wife), the Order would have accepted that relationship had it become knowledge.