Why did he leave the party early?

He is dating another girl, he chose her instead of me, and before and during their relationship which has been going on some months now, he would still tease me, stare at me, make suggestive remarks, eavesdrop on my conversations with others. We don’t really text these days. Anyway on Saturday night I left the bar with a guy I’m dating and we came back later in the evening and my male friend seemingly left not long after we did. He was there with his girlfriend that night but even so would eavesdrop on my conversations whilst simultaneously being all over her and try to get my attention. What do you think happened?
Why did he leave the party early?
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