Is it ok to have lunch with an old flame when you are in a committed relationship?

My boyfriend met an old friend who use to date my boyfriend sister along time ago. This guy is married and said his wife was ok with him having lunch with my boyfriends sister and asked my boyfriend to give his number to his sister and he did. I made a comment that it was not right my boyfriend said there was nothing wrong with it that he just wanted to talk about old times with his sister plus his wife was ok with it. I said he could be trying to spark up an old flame my boyfriend got upset and said he would do the same thing if he ran into an old flame. Am I crazy ? he doesn't like me dancing with his friends when we go out but he thinks going on a lunch date with an old girlfriend is fine.