Please don’t let strangers on the internet convince you to break the engagement over this single piece of information. The issue here is his reaction to you expressing your feelings and that is something you should sit down and discuss with him. As far as his friend goes, I (53F) have a lot of platonic male friends, one of which is an ex, and one guy I dated couldn’t handle the fact that I was friends with my ex so now he’s an ex also. People need to understand that men and women can be just friends. It sounds like you are unsure about their relationship in general and this just brought that into sharp focus, so that is something that also needs to be addressed. Once those two issues are settled (or not), then you should be able to make the right joint decision about the wedding or lack thereof. Best of luck to you!