I remember this novel very clearly. The mc is a cultivator. I think the very first scene was him losing to this other guy, who I assume was the og protagonist. The MC meets the ML, who is a transmigrator, and they go on this small journey. I don't remember the context of why they did but the go into this cave, and then they meet the og protagonist and this girl. I didn't get far into the novel but I remember some comments mention how the mc is really possessive
Haven’t read it, but the summary sounds similar: Let’s Talk About That Guy Who Transmigrated to Pursue Me.