Though “so” may be used this way in casual speech, “very” does seem better, unless the speaker is placing emphasis on HOW distant the friends have become instead of the fact that they are becoming distant at all.

The wording is a bit awkward towards the end of the sentence, and I would tend to agree that “becoming so distant from me” would sound better as “distancing themselves from me”. However, “distancing themselves from me” implies that the speaker’s friends are consciously making the decision to stay away physically and/or emotionally; whereas, “becoming so distant from me” can mean the speaker does not know whether the friends are doing this intentionally or not. Perhaps it is circumstances beyond anyone’s control, such as busy schedules.

-MM

They’re not including you in things like they used to.