I almost feel ashamed to be joining in on this discussion coz its a sensitive male issue but anyway.
Sister, what you need to understand is that at the age of 25, your brother is a man! Im sure he is aware of whats right and wrong Islamically, but sometimes people cannot restrain themselves, so it leads to these things (and from what I understand, he is not really 'womanizing'). This is something that should be kept as private as possible, it should be between him and God. Its unfortunate that you had to find out about your brothers 'personal life', but let it remain that way.... personal.
The consequences of making it a family issue can be devastating!
You may very well ruin your parents relationship with him, as well as your own, and you may very well mess up he's whole impending marriage if things leak out. (Btw, as long as he has not 'been' with a female he is still classified as 'pure' in some regard). So after all this embarrassment, what do you think a man would do? Apologize to all and stick around knowing that he's entire family knows about his darkest weakness? I don't think so sister, its highly possible he would leave home or do even worse (depending on his mental plane)
Maybe a nicer way to have dealt with this situation (keeping in mind that you have to respect him as your older bro), would have been to leave an article or booklet regarding this topic from the Shar'iah point of view, where you found he's collection, and keep the whole thing anonymous.
But anyway, please, think about the long term effects your actions could cause on your family. If you have already sent him the email, then khalas, you cant undo that, but don't pursue this any further, and may Allah (swt) guide us all.