ER: Doug tells Carol that he loves her, unfortunately at her engagement party with Tag

[trans8010]

When Doug sees Carol happy with Tag he cannot bear it and he reveals his feelings to Carol who also feels the same way but will not open her heart again on a profession, fearing he would just hurt her again. This is probably true since we learn later on his absent and abusive father spawned his commitment fears, and everytime he finds stability he sabotages it because of this fear. It was only a matter of the bad boy confronting his demons and maturing could they finally be together.