How do adults feel after their diagnosis?

Hi everyone.

I am new to the forum and have what I hope will be the third and final part of my assessment at the end of next week.

I was teased by colleagues at work about being autistic about 10 years ago (I am now 45), I read up on Aspergers on Wikipedia and it was like reading my life story.  I never took this any further though.  My wife did some training last year on working with people with autism, and identified that I had many of the traits.  We did a simple 10 question test (10/10), then a 50 question test (47/50), so knew if was something to investigate.  I have had an initial mental health type assessment, the first part proper of the autism assessment, and have the next one next week.

My wife has been so supportive and so have my children (aged 11 and 8) who we felt we needed to tell about the assessment.  However on speaking to my father and sister (my mum is sadly no longer with us), they (and I appreciate it may have been a shock), pretty much just didn't believe me.  When I went through the questionnaire with my dad he pretty much just said no to every question, although when I explained how I felt on some of the questions, his replies were that he felt the same (but that he was not autistic), or that "loads of people feel that way".  I tried to explain that it was the number of situations that I looked at in that way, and the links between them that pointed towards me being autistic. 

So I am wondering in this period before the next assessment, how others felt before and after?  I am hoping that getting the diagnosis will be a positive thing, and will explain a lot of the reasons I feel and act the way I do, but I have also read about people feeling a sort of grief that they only found out so late in life.  I wouldn't change my situation for anything, but I can understand I may feel something when I look back at life perhaps being more difficult than it needed to be?

Would appreciate it anyone would take the time to help me through this period, with their own experiences, thanks.