Like you, I'm relatively new to all of this, but I would say that it sounds like you two have deeper issues. I wouldn't look at adding relationships as a balm that will make all that just go away. If I were you, I would feel weird about opening up your relationship when you're still not being completely honest with him. How can you expect to be honest going forward? It's like a boil you've got to lance before you can heal and move on. What you described with the friend suggests to me that he might be having the same issues. That doesn't mean you're ready to open up your relationship; it probably means the opposite. I'd say you need to straighten out things between the two of you before you go adding anyone else into the mix, especially with two small children involved. I just went through a divorce with three small kids, and it tore my heart out.
Honesty. Have it out. One way or another, you'll figure out whether you two should be together. Figure that out first.
"I'm terrified beyond the capacity for rational thought."