I have been meaning to talk to you.
mean to 是“打算做”、“有意做”的意思,意思是：我已经在打算和你说话了也一直这么做着啊.
但我认为在口语中不太常用（可能吵架后会用,毕竟现在完成进行时这种复杂的时态实际口语中用得少）
We are supposed to be able to do our preparation and mark in that office.
be supposed to表示：应该 = should
我们应该可以在那间办公室做准备工作并作些标记.
Jack constantly has students coming in to get help with his couse.
have sb.do/doing 意思是：让某人做某事
杰克不断地让学生们进来帮助他课程的学习.