Why would the mother of my children not want to spend time with her children?

A couple months ago, my partner of 17 years let me know she may not want to be with me anymore. I have tried to do all I can to salvage the relationship because I still love her and because I want to keep our family together. We are still living together, even though she wants me to move out, at least for awhile, in the meantime she would rather go out, text or talk on her cellphone then spend time especially with our 4 year old son. She has left me to watch them at the last second many times because she decided or just "had" to get out for awhile. Last week, from Tue - Sat, she spent about 3 hours w/him, I took him and our 8 month old daughter away for the weekend, so she could have her space, even though I and my son wanted her to come along. Now the next weekend, she lets me know that she may be going away for the weekend without any of us, I asked her why would she want to be away from them again for that long, she was never like this before that day that she told me about us, having children was the most important thing in her life, we did everything together, as a couple and a family, and now she would rather go and get drunk, etc than be with her family. I care for her so much, love her and worry about what she is doing and that she is going to hurt herself in some way, not on purpose, but just the way her life is going. I am 42, she is 39, so it's not like we are young and partiers anymore, we are parents of 2 young children that should be our focus. I am willing to do anything to salvage our family, save our relationship, but I actually worry about our children when she has them alone. She forgets to brush his teeth, leaves food out, leaves the house a mess, she'll let him wear the same underwera for a couple days, fail to give them a bath when they should have one, etc. Could there be a reason for this, besides the way she feels towards me?? Please help.