Sandy - When your H says he's still "in love" with OW, what I think it really means is that he misses that dopamine high.
Antidepressants would probably help him, but since he hasn't gone for counseling, what else could you do to boost his levels? Is he exercising? What can YOU change to make yourself or home novel, interesting, new? Will he take vitamins and fish oil?
And meanwhile, you need to LIVE YOUR LIFE! What are you doing that's fun for YOU??? Don't let his depression drag you down too. What have you always wanted to do that you've been putting off? What adventures await you? Start going out with friends, take a class, learn a new instrument, don;t put YOUR life on hold one minute longer.