Re: Wife wants to be alone? What does that mean?
Have you heard of/read the book The 5 Love Languages by Chapman? It is interesting that she doesn't believe you understand her and you also say that you don't. This book may shed some light as its base is finding out what makes you/your spouse feel loved. From your post, it sounds as though you do acts of service (helping around the house, with the kids) and gifts (flowers) to show your love but she may be needing 'words of affirmation' or something else and not feeling truely loved even though you are doing what you know to show it.
How are you with affection? Hugging, kissing, cuddling? Complimenting her? If those have been lacking she may feel you don't desire her (coupled with porn this can make a woman feel unloved)
If you have those things covered, I would guess it's just having close conversations...not the daily finances, kids, stuff but the sort of things you talk about when you dated her...For some, knowing their spouse is still interested in them, their hobbies, work, hopes and dreams makes them feel loved.
Just some things to consider.