Hahaha... this was also in that post by Tas... Kyle was 6 when Michelle left—the Jim says it in Wipeout when he's recalling that Kyle lent him his Mr. Squishels for the night so he wouldn't have to sleep alone (Aw, six years old and already a sweetie! lol)
And it's implied that he only arrested Amy once, when she was protesting the demolition of a "a 200-year-old piece of Native American architecture...raping our town of its history" (Heat Wave) She's held a grudge against him since then because she was only 18 and out of all the people he could have arrested he picked her... which we find out with her on HW that it's because he thought she was cute...
Then they realize they have a bond... both single parents whose respective spouses left them (though in Wipeout it's hinted that Amy never married Maria's dad—she calls her mother's mother Grandma Deluca) and who are now having problems communicating with their respective children...
They go on skirting around a relationship (he's too busy with work, etc) this lags until Valenti gets fired and Amy comes to help him bounce back from his funk (can't remember the ep...?) Things look promising, then the disaster of S2 happens (Alex dying and Tess being blamed for it) and by S3 the authors kind of forget Amy existed....
Hope that helps!
I don't believe there was ever any mention on *why* her father left. I remember that there were vague spoilers floating around about the possibility of having him return to Roswell as an FBI agent and use Maria to get close to the pod squad, so I think they probably left it wide open very deliberately.
