The problem isn't him - it's you. Getting concerned over text gaps of 4-8 hours is unreasonable. He's busy, you're busy and life can't revolve around texting.
How about calling each other once a day and having a voice good chat?
- - - Updated - - -
Another suggestion: If you really prefer text over voice, say to him "I know that sometimes text conversations start and then life gets in the way. But so that I'm not semi-waiting for a text, could you just send me a quick message to let me know you'll be dropping out of the conversation for a while?" Something like "later" works fine.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.