Why does my boyfriend always fall asleep on the phone with me and not making enough time for me?

First I'd like to clarify my boyfriend and I have been in a long distant relationship for 3 years now. Were great together but I get mad when I'm talking and he starts dosing off I personally can't work do to medical reasons. His day starts at 5am and doesn't end till 11pm we go to bed together talking till 11. He works a physically hard job in yhe heat and is attending online college I know he's busy and he does try to talk when we can but it annoys me that mid convo he does off or forgets what we were talking about.

Why does my boyfriend always fall asleep on the phone with me and not making enough time for me?
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