what would you do?

well, that is tricky,isn't it. even if ou do not have any feelings for your ex now, it will surely make you feel a bit jealous now,isn't it. and , if she put an end to the relationship, it might just be lot more difficult for you. i guess, you should totally ignore thinking about them and concentrate on your current partner.

you should encourage him, and giv him some tips, unless your ex is very bad

Hmmm...it really depends on the fact that how my relationship with my former girlfriend broke up? If it was me who broke the relationship, I may have a milder reaction if the news comes up that she is in love with a person familiar to me; however if it broke from her side and now she is dating my friend, my reaction would be stronger and I will feel jealous....I might even go crazy and speak to her and say something nasty...cheers...you have a started a very good discussion !!