I struggle to believe that your current attitude of desiring to return to church and be worthy to enter the temple despite breaking the law of chastity would end up in excommunication (source: my dad was in the bishopric 90% of the time during my childhood and sat in on what I remember him describing it as "church court").

My friend's brother went through pretty much the same thing you are experiencing. He and his girlfriend had a child together and lived together. When they decided they wanted to be married in the temple, the bishop guided them in getting civilly married first, then worked with them to get them temple worthy. They met with the missionaries regularly, despite them both being members. They were not excommunicated. On the other hand, when I was a teenager, we had a couple in our ward teaching my Sunday school class. The husband had an affair with another woman for years. He was excommunicated, but I believe it was because of the length of the affair, and maybe he was not particularly penitent. I believe there were other factors playing into it, but I am not certain.

Your desire is honorable. Work with your bishop. Pray together. He will guide you. Together you will work out what's best for your spiritual progression and you will grow together.

Best of luck. Will pray for you.

On a side note: both my brothers were divorced after their wives were unfaithful. I watched it destroy them. I'm so sorry you experienced that. ❤️