My boyfriend got mad at me for not saying I love you?

My boyfriend and I were texting late night and I went to sleep a couple mins later. The next day I opened the messages and it had I love you in the end, but I responded with, I'm up now. He then got mad at me because I didn't say ily back and that he has to "always beg for it". I honestly didn't mean to ignore him. What do I do to make him less mad

My boyfriend got mad at me for not saying I love you?
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