The most obvious that I see at present is that tr Saturn Rx is - and has been for a number of months - squaring that quite difficult Moon-Saturn conjunction in the 12th. Note also that tr Saturn has been going through his 3rd for a while now, so he is only interested in good friends who can be relied upon. Even so, he may feel that he hasn't a friend in the world, even if he has. Unfortunately, after a marriage breakdown, he is `regrouping'. He no doubt is suffering from a loss of faith in everything there is, and the Saturn-square-Saturn is bringing him face-to-face with a truth he may not wish to face. Saturn's transiting opposition to Jupiter doesn't help, as what he now has to face is something he just seems unprepared for.
Added to what Saturn is getting up to is tr Uranus opposing the Mercury-Pluto conjunction - so he may actually be having difficulty in `keeping up' with what has happened in his life, and how to approach his life from now on.
Your friend is no doubt still grieving the loss of his marriage. This is one of the major losses which many people have to contend with - in some ways it is worse than had their partner died. Grief has its own timing, and everyone is different.
The best thing you can do is to leave him be for now, but let him know you care and can offer company if he needs it, or an ear, or whatever you have to offer. Note also that many men feel a deep sense of shame and failure after a marriage breakup - this may well be at the source of him isolating himself. Only he can deal with this.