<human>: Can you condense the text into a few key points?

My boyfriend will have days where he is feeling down and I (21 f) won't hear from him all day until late. It hurts me to feel that he can't warn me that he needs time alone but worse that he feels he cannot talk with me about it. Is it normal for guys or introverts to be like this? I just feel like he never shares any feelings with me unless they are romantic, but if our relationship is serious and we want it to last, shouldn't he be able to be open with me about how he feels? Maybe I could try to cheer him up? He has cheered me up before when I was really sad. I mean if we were to move in together/get married, is he just going to hide from me when he is feeling low? We are in a long distance relationship so the phone is really the only way we have to communicate, and we have been so busy lately our communication has already been strained. I tried to bring it up to him and he said he was drained, but I am thinking 'all day? Why not take a nap then?'. We have been together for about 6 months but have dated before over a year ago. We are in a long-distance relationship and don't talk often anyway, so not hearing from him for like 6 or 7 hours AND not being warned that he just needs time alone puts me in the dark. We see each other one day about twice a month so he shouldn't feel smothered.
<bot>: Is it healthy or normal to have a partner who secludes himself from you all day when he is having a bad day?