Can you argue improper service, if you were served with the summons, and were told by your spouse not to worry about it because he had changed his mind and began acting as if the relationship was on the mend.
Then he began drinking heavily and dating another woman, which was not unusual, but he never mentioned the proceedings again, and continued to use terms of endearment when talking to me, attended family events and shared a home with me.
On January 12, he handed me a signed Default Judgement, which included a custody order which states that he has custody of our son.

History: I have filed 4 separate summons and request for dissolution, however, each time we have worked out the relationship, throughout our 15 year relationship he has dated this same woman for over 8 years.

Because I lost my mother, and I was still living with my husband, I was under the imprtession that we were working things out. Then, on January 12th, he hands me a default judgment which states that I would be moving out on January 1, 2011 and my alcoholic husband has custody of my minor child, what do I do?

Not likely... You were served... properly.

Now if he said something different afterwards... you were still responsible to confirm if there was any changes to your court date. It seems you made the mistake of not doing so.

Now morally what I think about how it was handled is immaterial. Once you are assigned a court date... one never assumes anything changes without written notification by the court or having confirmed it in person with the court Clerk.

But you can still try. Just be aware that it is now a uphill battle as the original ruling has to be proven improper or defective. And a no-show isn't a mistake by them.

Very doubtful. If that is your only defense, then you have no other choice than to try. But if you can prove he said that he had dropped the case, ( proof the court will accept as evidence) but if he merely started acting better that is really not proof of anything.