Since is sometimes confusing because it can have several meanings.
(1) It is very common to use since with the simple present perfect tense. Here is one construction:
- Since + definite point in time or period of time + subject + verb phrase in the simple present perfect + more information.
Since January of this year, she has earned over $45,000.
She has earned over $45,000 since January of this year.
Since that time (1941-1945), our town has grown enormously.
Also consider this interesting example:
He got out of the military two years ago, and has since gotten married.
(2) Words and phrases of unfinished time can refer to future, past, or present time; unfinished time sometimes takes the present perfect tense or the simple past.
Examples of unfinished time would be: today, this morning/afternoon/evening/week/month/year
I had bacon and eggs for breakfast this morning.
(simple past – it is still the same day referred to, but the event is in the past)
I had bacon and eggs for breakfast earlier this morning.
(this makes the current time clear – it is still morning)
This morning the songbirds have been very loud.
(present perfect – the current time is still this morning and the action may continue; the action may be going on at this moment)
(3) We often use the simple present perfect to talk about an action:
- (1) that started in the past and continues at the present time
- (2) whose exact time in the past is unknown, vague, or unimportant
- (3) that happened in the past and is important now
Notice the use of the words ever, for, since, ever (refers to the more distant past), up to now, already, so far, yet (yet is only used with questions and in negatives), as of yet, never, recently, and just.
The simple present tense has many uses. For example:
Life Experience / (sometimes expressing how many times?)
We can use the simple present perfect to talk about life experience. We can use it when the specific time of an action is not important. Moreover, the number of times an action happened may be omitted. The fact that the experience occurred or not is often what matters most with this usage of the simple present perfect.
Has he ever eaten Korean food? (life experience, indefinite time)
I have been to Laos many times. (life experience, indefinite time)
I have been to Warsaw. (life experience, indefinite time)
Have you ever been to Japan? (refers to an indefinite time)
We have already seen that movie. (life experience, indefinite time)
The boss has called her many times. (indefinite time in the past)
I have never been to Shanghai. (never)
Has she ever been to Moscow? (yes or no; at any time)
She has been to China twice. (how many times?)
She has recently been to Japan. (life experience, indefinite time)
Mr. White has never seen snow. (life experience; indefinite time)
That was just one of the ways to use the simple present perfect tense. Here are two more examples:
I have eaten at this KFC many times since last May.
She has lived in London since she was five.
And, what is the difference between these sentences:
- It's been so long since I talked to you!
- It's been so long since we have talked!
- We have talked about this problem since noon – that's about enough!
The first sentence points to a finished event in the past. The second sentence is incorrect. The third sentence is a standard use of the simple present perfect.
The sentence shown in your question should be:
(U.S.) It has been so long since we talked.
or: It has been so long since I talked with you.
(Brit) It is so long since we talked.
or: It is so long since I talked to you.