The prevalence of collaborative learning in online virtual environments is on the rise. It is vital to investigate the effect of emotional interaction on the learning engagement of students. The university students who participated in 16 h of online collaborative learning responded to an anonymous survey. The instruments included Collaborative Learning Emotional Interaction Scale, Loneliness Scale, Positive and Negative Rumination Scale, and Learning Engagement Scale. The mediating and moderating roles of variables were tested. Both positive and negative emotional interactions in online collaborative learning positively predicted learning engagement. Positive emotional interaction can inversely predict loneliness, while negative emotional interaction has a positive effect on loneliness. Loneliness inversely predicts learning engagement. In the low level of positive rumination, loneliness has a significant inhibitory effect on learning engagement, and the effect is much greater than that in the high level of positive rumination. In online collaborative learning, loneliness mediates the effect of learners' emotional interaction on learning engagement. The level of positive rumination moderated the connection between loneliness and learning engagement, the second part of the mediation model. We can begin by increasing learners' positive rumination and reducing the detrimental impact of negative emotional interaction and isolation on learning engagement in online collaborative learning.