@swtpea
Sorry this is so long...
How do you feel about your man?
How do you think your man feels about you?
How often do you talk, text and/or see your male bff?
Is your male bff the main source of your man's insecurities?
Has your man met him?
Does your male bff have a woman? And if so, have you and your man met her?
Answers to those questions would present a better picture as to which person (him or YOU) red flags should be thrown.
I do believe that "sometimes" the person who is snooping is the one doing dirt. However, also I believe a person can behave in suspicious/untrustworthy ways to cause their partner to feel like something isn't right. I don't consider that to mean that person is insecure, just simply he/she may not feel the relationship is secure.
The whole dynamics of you and your male bff relationship should have changed as your relationship with your man got serious. Not saying the friendship should end but daily communication or early morning/late night texts and things of that nature are big No Nos to me. A lot of women run to their friends for comfort, support and to just vent when their man pisses them off. Little things and big things. Even though that's not a good idea, it still happens more often than not. And for a man to think/know his woman is running to another man to share things about his failures, insecurities, or whatever, would be a huge blow to any man (or woman). Creating intimate bonds, sharing secrets, valuing your male bff's feelings over your partners is not a position I would feel comfortable in.
You may need to think about whether or not you really want to be with your man. It doesn't seem like you do. Something else to think about is how you really feel about your male bff and how he feels about you. If I had a male bff, just out of pure respect for my bff, his woman and their relationship, I would fall back unless his woman initiates or is involved with our communication. I can "possibly" understand someone 25 maybe even 28 years old or younger not getting that but 30s and older is much too old to not see the potential drama that could cause.
Finally, to answer your question, I feel both of you are overacting. Honestly, if I were him, I would probably call off the relationship. I wouldn't want to be with a person who blatantly disregards my feeling about their relationship with another person of the opposite sex. That is disrespectful on your part which causes the lack of trust on his.