QGD Black - Cambridge Springs Defense
Time control was 3|17.
Hmm, in hindsight, playing 18. ... Re8 was probably wrong after obtaining the better bishop. Should have played 18. ... Rd8 instead I guess.
I probably should have played 25. ... Kh7 and 26. ... e5. Maybe I should have played moves like 8. ... Qc7 eyeing an e5 push? Or is a c5 break the idea?
I was very low on time when I played 34. ... Qxd3. I couldn't calculate much after this point. When I played 35. ... d4 it was a mistake, I didn't notice his knight was defending his rook.
This is not the Cambridge Springs, so none of the typical Cambridge Spring's ideas would have worked.
This is the Cambridge Springs via its traditional move order:
Notice the pinned knight on c3 and the lack of a bishop on e7. This allows Black to play Ne4 and possibly follow it up with Bb4. Another secondary idea is that the Queen indirectly attacks the bishop on g5 making the natural Bd3 a mistake.
The Cambridge Spring's is trappy, but not 100% reliable and I like White after 1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. Bg5 Nbd7 5. cxd5 exd5 6. e3 when White has a good exchange variation.

aggressivesociopath is right, as soon as you played 5...Be7 you no longer were in the Cambridge Springs defense. I'm not calculating this exactly but after 6. Be2, you could have tried 6...c5 or aimed for ...c5 later on.
Even 6...Ne4 comes to mind, seeing that white is not covering that square with a bishop on d3 or a knight on c3.