以前养过狗叫做前男友
[yĭ qián yăng guò gŏu jiào zuò qián nán yŏu]
It's humorously implying that the user's ex-boyfriend was as loyal and affectionate as a dog which is sometimes said about a great guy who treats the significant other very well. But since they are no longer together, referring to past boyfriends this way also hints at a touch of sarcasm.