Two things jump out at me. One, you guys got together very young. You were 18. In this day and age, people grow up slowly, and don't really stabilize their values and goals until later.
The other thing is that you say you "always had intimacy issues." That sounds to me like a fatal flaw. You can't have a successful long-term marriage if you have intimacy issues.
As for him being nice to you -- it's not because he wants to get back together. He wants to be nice to you because it helps him feel less guilty about breaking up the marriage.
Me: 50, MLC/WW 45 Young kids Nov 2015: BD1 Apr 2016: BD2 Jan 2017: W filed Feb 2017: D final