его поведение было странным, когда

его поведение было странным, когда мы встречались.
потом оказалось, что в тот момент, когда мы встречались, он всё ещё был влюблен в свою прежнюю девушку

Results (English) 1:

his behavior was strange when we met.then it turned out that at a time when we met, he was still in love with his old girlfriend

Results (English) 2:

his behavior was strange when we met.
Then it turned out that at the time when we met, he was still in love with his old Woman

Results (English) 3:

his behavior was odd, when we met.then, at the time when we met, he was still in love with his old girlfriend