I hate to ask this because you seem to be pretty sad about this right now, but, did he ask you to move with him? It occurred to me when I read the OP that he is, 1)under A lot of stress at work, 2) on a pretty major drug, (the worst experience in my life drug-wise, was coming off Paxil -had Horrifying panic attacks for months after withdrawing) so consider that the drug is having some serious effects on everything for him, 3)sees problems in relationship you were unaware of, that 4) would make him pull away as he weighs job stress, moving because of said job, maintaining a relationship, and likely not wanting to upset your life too much as he goes through this hard stuff.
All you can do is let him know you love him, miss him and will be here when he is able to spend time together. No guilt, no pressure. Be sincere that you want him to take the time and space he needs as he juggles what sounds like almost more than he can bear. You don't want to become something he feels is just one more thing to deal with...right?
What is that old saying? If you love someone let them go. If it is meant to be he will return. He will love you for taking the pressure off in at least one area of his life.
Also, if Omega 3 is beneficial for this, then perhaps try Flaxseed Oil. It is easier for the body to assimilate and has many other health benefits as well. Perhaps you can see if he can get B-12 shots or take a combinations of stress vitamins...the B complex really helps with this.

You sound like a lovely and loving woman.

All the best to you as you work to help your very wonderful man...