I have experienced this before.
Think of, or better yet, write down all the little things that you argue about with him, and have him do the same for you.

Analyse the list carefully and I assure you you will realise that there is a theme that runs though the list. You will then be able to identify one or more underlying causes for all the little arguments that you have.

For e.g if he forgets to pay the bill, he overspends, he stays out late, he doesn't help with cleaning up...these may all seem like isolated issues but when you look at how he handles them all it may show ONE major problem - that he may not be fully dedicated to you , your relationship and your son.