Marriage Difficulties/Not Yet Diagnosed ADHD

I am brand new to this site and this is my first post...sorry in advance if I ramble.

I came looking for a site where I could find some help for my marriage. It's currently in big trouble. Over the years my husband and I have had a great deal of issues I've seen other people posting about: financial strain, under-appreciation, disorganization, blaming each other, etc. However, I have recently discovered that my husband has been texting other women secretly, behind my back and when I realized what was going on lied his face off about it. I'm pretty sure that the only line that has been crossed is secretive flirting, but I have no way to be 100% positive. This is the second time we have been down this same road. The first time was about 4 years ago. On top of all our usual struggles, I feel like this is a last straw. I'm crushed. I feel like I've invested everything into our marriage and family and he's tossed it away like it meant nothing. 

For a little more of the back story, all 3 of our children are diagnosed with ADHD. I have assumed I've had it since I was a teenager, but never did anything about it. I've always recognized it in my husband, but he has vehemently denied it...until now. 

Since our current state of marital distress began two weeks ago, he has now said that he is willing to seek diagnosis and treatment for ADHD. Ironically, in last week I received an email newsletter about the ways that ADHD can wreck a marriage. I forwarded the email to him and he totally saw himself in it. He feels horrible about what he's done and he's promising the world to try to make everything right. But..

How much of this can I realistically expect to change by having us both diagnosed?