To tell or not to tell?

Tell. B is a co-worker of mine. He lives in the same apartment complex as one of our (female) clients, C. He's always had a crush on her and they became friends. C was taking a class with me and started flirting. I asked her about B, and she dismissed him, saying, "B is my neighbor." Now I know I shouldn't have gone along with it at all, but I did. She was cautious because I'm newly divorced (since December), and wrote me emails that said things like "Once your heart has healed we're gonna get together." She invited me over twice to visit. Nothing happened. After that she disappeared off the radar for a while and then suddenly today B was telling me they were buying a house together and getting married. What?! I talked with another co-worker about it and she agreed that C seemed awfully unsteady and that maybe B shouldn't go through with it. I decided to talk to B. He argued with me and said "I already talked to her about you. She told me she wasn't flirting with you, but you took it the wrong way." I said I was experienced enough to know when I was being flirted with. He told me I was mistaken, that she was just being nice. Now she was lying to him and making me look stupid. That made me just mad ehough to do something maybe I shouldn't have -- I let him read the emails she sent me. I wasn't trying to show off or make him look bad, but I didn't want him to get into a bad situation. He turned white, and quietly apologized. I felt bad for him, but I still think I did the right thing.