<human>: My (18m) friend (17m) and his gf (17f) broke up about three months ago. I've known her for about a year and him for two years. 

Me and her were very good friends even before they started dating (only dated a few months) and about a month ago she began hinting that we should date. Anyways, this past Friday night we went to a party together and ended up hooking up and now we aren't dating yet but are in a fwb scenario until we decide to take it further (we've both admitted feelings for eachother and have both said we should date).

Now our mutual friend (24m) is mad because he says it is wrong of me to be having sex with/soon to be dating a best friends ex and will not talk to me, after having sent several angry text messages calling me various forms of a piece of shit friend and scumbag. I've talked to friend 1 about it and he's completely fine with it and doesn't care, he even encouraged it. 

As far as I see it, if you and someone break up it shouldn't matter who they then have sex with or date, since you're done with them, but I guess some people think otherwise. 

So Reddit, what's your advice?

Can you give me a shortened version of the text?
<bot>: Hooked up with a friend's ex, potential to begin dating soon, friend doesn't care, mutual friend thinks I'm a scumbag.