I don't think you should ignore or "forget" his birthday. Believe me, I am all too familiar with the dynamic of H doing something provocative, W reacting, and H distancing because of W's response ( while the behavior doesn't get fully addressed). Stay strong and set boundaries ( even if that means separating), but if your ultimate goal is to save the marriage, try not to let the hurt/anger/resentment spill over into the good parts of life ( like birthday celebrations). JMO.
