Student or Learner
What is more natural to you?
1. What he was going to gossip about to Elvira'
2. What he was going to gossip about with Elvira.'
When you speak to someone, they listen, you speak; e.g., The boss wants to speak to you. When you speak with someone, you both speak; i.e., Your client's on the phone and she would like to speak with you. The verb gossip with/to works the same way. So, you see, both gossip to (tell to) and gossip with (share with) are English. Whether one is "more natural" (i.e., more common?) than the other depends on how often the person has heard the phrases.
Ex: Do you know what he was going to gossip about to/with Elvira?
Does that help?