My boyfriend said he doesn't like that his female best friend is having intercourse with her boyfriend. Could he possibly have more than just platonic feelings for her?

Background:

I am 23(F) and he is 25(M). We have been dating seriously for 2 years now and have always sought the goal of marriage in the future. He has been friends with his female best friend since they were in middle school but has been close with her for the past 6 years or so. He comes to her for advice about most things and she the same for him. I have met her and she is a very nice and kind person. My boyfriend says she is someone he loves and respects and wants in his life for a very long time. She had been dating her BF who is also a friend of my boyfriend's for the past 6 years as well. They recently broke up and her ex boyfriend met up to talk with my boyfriend about how he did not like the relationship my boyfriend had with his ex. My boyfriend and his ex(my boyfriend's female best friend) would always talk to each other about the relationship and he did not appreciate the fact that my boyfriend was her close confidant. After the talk, my boyfriend was venting to me about how he did not agree with his friend's views about his involvement in the relationship with his ex. My boyfriend said, "my friend told me that he did not like the fact that I was talking to his ex during their relationship and he was mad at me about that. Well I didn't like that fact that he was fucking her but I didn't say that. I don't know why he thinks that our friendship was not ok. We talk to each other because we are closer than I am to him."

In that moment I was not sure what to say however, my boyfriend said it with a lot of firmness and he was obviously angry about his friend. I didn't want to interrupt and wanted to let him vent. However, that statement has stuck with me and I am not sure what he meant by it. Personally I think that even though they are close having that kind of opinion about your friend is a little pass my line of comfort. I recently confronted him about it and told him that what he said made me uncomfortable. He quickly defended himself by saying he meant it as a joke and that he feels as though I don't trust him.

I think their friendship is great and have never questioned him at his word about their friendship. It has only recently changed due to this statement. The way he talks about her to men and how involved he is in her life is starting to make me think otherwise. I personally think he has always had some sort of feelings for her because of how close they are. He has admitted to having feelings for her in the past (high school) but had never acted on them because she was always unavailable. She is now available after a very long time and I think he might be confused about how he feels about her. Could he possibly have feelings for her that are more than platonic? Am I over reading the situation? I would like to thank everyone in advance for your help.