oh my!! i've inherited a pre teen!

my fiancee and i got custody of his 12 yr old son 2 months ago. i was use to getting him every other weekend and have had ups and downs (more ups). but his mom decided that she did not want him any more and dropped him off with no looking back. her excuse was he is to much to handle at this age! how can one as a mother just unload a child like luggage and forget about him? i dread mine growing up and leaving?! i hate leaving her when i go to the store! to top it off she is late turning in all paperwork to make it official and still is collecting his child support for her liking. the poor boy is not even up to date on his shots (last ones at age 5) has not been to the doc/dentist in years and her only answer is i forgot, or i have younger kids that need more care and attention! i remember being a teen but never a boy. she has allowed him to see her being in a abusive relationship for years so he has no respect for women and has even struck her. i understand he is going to need some work, but i don't think he is worth tossing in the towel. got all appointments made to correct those errors including a counselor to work on inner issues and learned traits that are not ok. any other advice from moms in this or a similar situation?

About Jen Henderson
Current: Fostoria, Ohio
Birth: May 09
On Moms.com since: Jan 18, 2014
Stay at home mom