Expressing how we feel to others helps us learn to recognize what we feel and to express it to others so we can better understand what to "do". Feelings are tools to let us know how we are viewing the world, others, and ourselves; they're kind of compasses (or, better yet, when used well, gyroscopes). The more practice we have recognizing and working with them (telling others) the better we get at orienting ourselves and knowing what actions we might want to take.

You said you didn't know why you missed T? Talking to T about missing her might help you better understand what it is about your life or relationship with T that makes you miss her so much. You cannot "do" anything about missing her, miss her less or less often, unless you understand why you miss her and you can only understand why if the two of you discuss the situation; otherwise it just stays in your own head and heart, a closed situation.