All's fair in love and war. If you are really interested in the
guy, just go for it.
If your friend is gonna hate u for it, so be it. Cos the fact is
they already broke up. So you have every right to be with
him.
But, most importantly, u sure he is interested in u
too?...Afterward he not interested, then u lost both a fren and
potential bf. 
So my advice is to confirm that the guy is interested in u first,
before u do anything more concrete like professing ur love for him.
