It depends on what you told your friend! If it was personal stuff , yes he would get mad. Some things you just keep private between yourselves. If it wasn't personal things, then I wouldn't worry about it as long as you told him it wasn't private stuff. Best to just keep things between you and him and avoid any trouble.
It sounds like you need to re-earn his trust.
It might not be easy, and it might take some time, and it's very likely that noone else other than you will know what it takes to get him to trust you again, but by the way your question is worded, I can tell that you realize there's been a breach of trust, and if you want to stay in the relationship - you may need to find a way to convince your boyfriend that you can be trusted once again.
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