Hi eblake00,
Welcome to the forums.

You realized this now. That's a hugely important step toward making amends. It's the "AHA!" moment.
For me, dealing with guilt means either making amends or, when that's not possible, paying it forward.
I think it would be good for you to tell your wife this, exactly the way you said it--maybe even print it out and give it to her in a letter. I would do it as information, not as an apology. Here's why: an apology implies external forgiveness. You first have to forgive yourself. Forgiveness doesn't mean that you're great all of a sudden. It means that you're back to neutral. What's done is done. It's what you do
differently that matters.
It's possible that doing this might cause an explosion from her; I don't know her and I can't say for sure. Sometimes, when people receive an apology they get flooded with feelings. So you'll have to be prepared for it.
Or you can say nothing and just make a silent resolution to either mend the past or, if you can't, move forward...and, like the saying goes, "don't do it again".
And if she asks why you're doing nice things for her and being on your best behavior, you can say something along the lines of, "A while ago, I realized how I've been acting and how it affected you. So I've been doing my best to be good to you. I don't expect it to make up for anything I did. But I don't want to keep doing the things I did before." I actually wrote that to someone before. Take what you will.

--Frayed
Do not take my advice before talking to your doctor/counselor/other professional. Depending on where you live, you may be able to find free, confidential care. Most importantly, sometimes your shrink can be wrong. Get a second opinion.