(Not a Teacher)
A) "I have been to Japan for two months./I have been in Japan for 2 months." = The speaker could have just gotten back from Japan or visited Japan 10 years ago. The timing of the visit is unclear.
B) "I have been to a hospital./ I have been in a hospital." = Both sentences mean the same thing. First sentence could imply the speaker has recently been treated at a hospital.
C) "I have always wanted you." = Suggests the speaker is not yet in a relationship with the person they desire or that speaker has just begun a relationship with that person.
"I always want you." = The speaker is currently in a relationship and reaffirming his love for this person.
D) "I always fight with you vs. I have always fought with you." = Both sentences could mean one of two things. The speaker and the other person fight together as a team, or the speaker and the other person always quarrel with each other. The only difference is the tense.
- For Teachers