Yeah, we slept together, I should've put that in the OP.

I've been thinking about this situation this week and I've developed a zen mindset about it - Things didn't work out for a reason, and if she gets together with my friend then they get together. Nothing I can do about it. There are other girls out there for me that would be a better match. As of now I'm keeping things cordial with him, but I've been closed off talking about my personal life and keeping things strictly business.

My friend also has some white knight tendencies, but I never really noticed them till now. In the past he's sided with girls when they broke up with his friends on a couple of occasions. Yesterday he mentioned he was texting about the plot of a movie with the ex of a good friend of his, even though the break-up was nasty as hell and fucked his friend up. I also remembered that his last long-term relationship was with a girl another friend of his had been with, even though once again that girl and that friend had a messy break-up. He's definitely thirsty and not against throwing close male friends under the bus for even the slightest whiff of pussy. He's got a great job and makes great money, but he's mentioned before he has a hard time meeting girls and has consistently shown to have no game knowledge. What better way to get with girls than to find those he has the most social proof with, AKA platonic friends or girls his friends have been with.