how much time is "normal" for a guy text back?

When I first started my relationship with my boyfriend a few months ago, we would talk/txt everyday. He would write me back within minutes, if not hours, or the lastest the next day. He introduced me to his mom, his friends, etc., even told me he was sure he wanted to marry me and i figured he was serious.

Problem is, he's a workaholic. Now he's working 70 hours a week, (16 hours a day, He pretty much sleeps 6 hours a day) ...he is filling in for another employee who got fired until a replacement becomes available. Usually he txt msgs me every day or every other day, and sometimes he calls me for 15 minutes inbetween shifts.

But when I texted him 3 days ago just to say hi and see how he's doing, I never heard back from him.

If he was really into me, wouldn't he find a minute in his busy day to at least txt me back by now? The fact that he is showing silence, I feel like he doesn't care anymore.

I need a guy's perspective please....

3 days isn't good. I'll put it off for a couple hours sometimes sure. I wouldn't say it means he isn't into you though, maybe he is just out of it due to his grueling work schedule. When I used to work that much sometimes I wouldn't want to talk, but not often, and not 3 days.