<human>: Ok to make this long story short, my best friend (zack) has no game when it comes to picking up women. I tried for years and years to help him, but he goes overboard and wants to buy then everything under the sun. He literally becomes obsessed with them until the tell him off. Then he goes into angry mode and resents them and hates then and does nothing but talk crap. This has happened at least 6 times that I'm aware of. And he's been my best friend for over 22 years. Zack has apparently tried to date my fiancée but came on to strong and told him off and he became very bitter and hateful towards him(all before me and her started to date). 
Now to today, I had my fiancées baby shower(we were planing on getting married in July but had to be pushed back cause of her pregnancy also due in July). Talking to zacks friend (mark) and his wife(Mary), zack has apparently been texting mary daily saying very hateful things about how "she's a slut" and "she is just a horrible person", for some of lesser hateful things he said. I saw some of the texts and can't believe that he would say such thing. I love my fiancée more than anything on this planet and cannot be happier with the way our life's are going. 
I'm starting to worry though about zack. I'm afraid of his attitude and hate towards her that this might escalate into something really dangerous. Zacks been the best kind friend throughout all the years. I've never seen him do anything remotely violent. I'm just not sure how to handle this. I haven't told my fiancée any of this yet cause we had a major issue with her aunt(maybe another topic I'll have to post tomorrow) cause this pregnancy hasn't been easy on her(many complications) and I don't want to put anymore stress on her. Is there anyway to defuses this situation with zack peacefully? Or if I have to tell zack off, how exactly should I do without really adding fuel to the fire? And this was longer than I had intended. Any and all advice is great!

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<bot>: my best friend had feeling for my fiancée that has since turned to an obsession of hate. No idea how to defuse this situation