To live happily in ignorance or sadly in reality
If you had a choice to live out the rest of your life in complete ignorance of everything (your strengths, your fears, your shortcomings, the things that hurt you, the people that hurt you), you would live in ignorance of your feelings, and if you're indifferent, selfish, you're happy.
The other choice is always knowing the truth: the truth behind why X happened in your life, the truth behind what Y actually thinks about you, why X left you, why, what, when and how. You would always know the exact truth. The real truth.
The original quote "ignorance is bliss" is from Thomas Gray's 1742 poem, Ode on a Distant Prospect of Eton College. The full original line is "Where ignorance is bliss, 'tis folly to be wise." So we can determine that living in ignorance is bliss, i.e. happiness, and that it's a mistake to be wise, to be knowing.
A statement
Suffering is coming no matter what, so knowing only means suffering twice. You can prepare for it and walk it through your mind, and then it arrives for both the prepared and the unprepared man. The prepared man suffers twice.
Thought experiment
If one day someone you love leaves you, and the only thing they leave behind is a letter with the exact reasons why they left, would you read the letter? The worst has already happened: they left. The only thing left to be attained from the letter is the reason, which will only bring you more pain. At this point you can do one of two things: read the letter, or don't. Burn it or hide it. You can't unread the letter.
If you choose not to read the letter, you live in ignorance. You are not more unhappy. The letter might contain your flaws, or the other person's mistakes, that might hurt you more. But you chose to live in ignorance, not letting the letter hold any power. The letter only has power when you open it.
In a reality where you did open the letter, you aren't in ignorance anymore. You live in the ground truth. Cause and effect. There is no such thing as a morally right thing to do, because the other person already left. They are not coming back. Whether you open the letter or not affects no one except you.
Stupid human nature: a symmetry
The person with the sealed letter keeps thinking about opening it, and the person who opened it wishes they hadn't.
So, do you choose to live the rest of your life in ignorance, maybe not completely happy, but not completely unhappy either? Or do you live in the ground reality, hurting yourself, being sad with what actually is, wishing you never opened that letter?