Sounds like you and I have very similar situations.... I left my husband of 10 years about a year ago, because he was cheating, (among other things) and it has been pure hell. he fought me on custody of our 12 year old son and has harrassed me to no end. Semi violent, had to get a restraining order, etc. At first we split time with our son 50/50 but our son didn't like that and wanted to live with dad because dad has no rules, etc. In our state the child can pick at his age, so I let him go. RELUCTANTLY. I ended up having to be on anti depressants because I was sad and crying all the time, obsessing over what was happening to him while at his dads, what he was hearing and seeing, was he going to school, etc. Did he still love me...so many issues. I like you feel empty without him. he's missed 12 days of school already, he's smoked marajuana, and his grades are failing. (mind you this is a child who NEVER got in any trouble or missed school, and made good grades) Sooo, I am doing everything in my power to take him back to court right now. Ahhh stresss. And the harrassment continues, even this long removed.
In the mean time, I hooked up with a very old friend from highschool.... the one that got away if you will...realized he is my soulmate....we were together for a while before the divorce was final we lived in different towns, etc. I got some of those same feelings that you have about it feeling temporary, learning things about him (and him learning about me) has sometimes been rough. But communication has saved us. We now live together, and my divorce is final, which has helped my insecurities alot. I however have never considered going back to the misery to make the ex happpy and be with my son. Although I want to be with my son more than anything. I just feel that being miserable not only affects me, it affects him too. How can he grow as a person and be a well adjusted happpy adult if he only sees misery around him? So I press on trying my best to get custody, and make the best of the situation as it is now. Make the most of your time with your kids while you have them. I've found that I have less time with my son now, but it's all quality time, so it's actually nice.
I know this is long, and you didn't ask for anyone's life story, but I just wanted you to know you aren't alone.