Are second marriages ever happy?

As a matter of fact MANY. Chelle's marriage has been restored for years, and they are very happy, also Lota is a second marriage and I know they too are very happy and blessed.

Does it matter if I had a church or civil marriage ceremony?

What matters is not what is legal but what God joined together. All of your questions really need the Lord to settle in our hearts, it’s not something anyone else can settle in our own hearts and minds. Also what you believe is often dependent on what you are seeking.

Many want to find what they want to believe “Ask and it shall be given to you; seek and you shall find . . .” (Matt. 7:7 KJV).

“But wanting to have their ears tickled, they will accumulate for themselves teachers in accordance to their own desires, and . . . will turn aside to myths” (2 Tim. 4:3–4). 

Hello, I have a doubt. Can you help me please with this doubt? My doubt is about the principle of letting go. Does letting go mean we also stop praying for our husbands and no longer asking God to restore our marriage?

Yes, that's correct. Here is the lesson and also testimonies to help you.
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I needed to seek God to help me to overcome to help me to let go of my fear and to be in complete obedience to Him. What a relief ... and it shows you what stage you are at in your marriage restoration. and letting go is the 1st stage~ Sasha in Trinidad

Daddy!! 

... I was able to start applying the principles immediately, especially the "letting go”. I had to do something - and to have practical advice about how to act upon this principle ...