With the same disclaimer as the others, that you check out with a LLL leader and or ped.....
I was struck in reading your post by the tummy aches, and around here there are some severe stomach bugs going around. If what your child has is a contagious illness, it makes complete sense that the child is instinctively nursing more and eating less. One of my children (weaned years ago) would eat SO little, maybe one piece of toast A DAY even after she recovered from the vomiting-for-a-few-days.
(This was scary but after about a week she is eating again...but still eating less than last month. This tummy bug seems to linger and ruin their appetite.) We've all had tummy aches lately.
Since nursing gives him mom's milk that is emotionally comforting, VERY easy to digest, sweet and tastes good, it would naturally be appealing to a sick (or well!) child. Nursing gives the child antibodies that destroys many "bad guys" like germs, bacteria, viruses, etc. Sounds like your child could simply be instinctively protecting himself.
Take the time to heal from your marriage before you move on with someone else. Make a list of all the qualities you would like in a new partner and then work on growing that way yourself. ~mandib50