Is he cheating on me with someone else?

My boyfriend is very caring, loving and always makes me feel good about myself, he's sometimes so good that it becomes difficult to believe.. He always fears doing something wrong and losing me.. He always says to me that he doesn't wanna lose me.. So we used to talk late at night sometimes, one day we talked until 1:30 at night, the next morning he said that both of us should sleep on time and he said that he's set his phone on lock mode and from now on, his phone will automatically get locked at 11:50 in the night.. We were talking yesterday and at 11:49 he said that 1 minute is left.. After that he disappeared at 11:50 and I assumed that his phone has got locked.. But I was skeptical and I checked and caught him online right after 10-15 minutes.. I dropped him a text that hasn't your phone got locked, he immediately went offline.. I deleted my text immediately.. Today, in the morning, I got a normal Good Morning text from him.. Why did he lie to me?

Is he cheating on me with someone else?
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