The Student Room Group
How do you reply "late"? Is this a texting conversation? :confused:

Maybe there's just nothing to be said. Maybe life is boring. Maybe you're boring. Maybe they're bored of you. Maybe they're bored of life. Maybe they're bored of your ridiculous conversation topics, and ton' have anything to say themselves. I dunno. Why don't you ask the person? It's more than likely to be nothing serious, but if it is serious (e.g. domestic problems, problems with friend/boss/relative/partner, illness, depression), you'll be glad you asked.