<human>: My (37F) ex husband (44M) and I share 50/50 custody of our two sons 8 & 10.  The boys went to their dad's place on Sunday evening as usual.  On Monday while dropping off some shoes at the school for my older son I discovered my younger son had lice.  Gross but now totally horrible.  This happened once before so I took my son home and spent an hour combing a lice treatment through his hair, shampooing, drying and combing some more.  I called my ex-husband to let him know so he could purchase some lice shampoo.  I explained that the treatment I had done was very thorough but I was concerned that a follow-up would be important to ensure all the lice were gone.  
I saw my sons and my ex on Wednesday night at a school event and no shampoo had been used yet.  I reminded my ex how important it is to keep this under control.
It is now Saturday night, my boys called to chat and still no lice shampoo has been used.  
The last time my boys had lice I treated it several times and informed their dad before they went to his house for the week.  They returned with bugs so big I was mortified.  I ended up having to buzz their hair off to ensure they were lice free.
I feel as if my ex is being totally irresponsible and not taking this seriously because he is just plain lazy.

Condense the text into a few key points
<bot>: Son has lice and ex husband is too lazy to do a follow up treatment.  Worried both kids will come home infested again.