I hate to hear you are having a tough time right now. You seem to have a good handle on what you need to do, but 2x4 time on DETACHING. The only reason today is tough (birthday) is because YOU have made this day out to be important. It does not have to be anything but a normal day. Even if you were in a strong M, the world would not end if you did not do something for her today, but next week, or next month. It is just symbolic because you have made it that way. I am sure you would give up 1 birthday for a lifetime with her. And for that reason, you need to detach.
Being in this funk does not help you mentally, emotionally, or even physically. And it certainly will creep into your interactions with her and facilitate making mistakes you would not make if you were detached. I know it is tough buddy, we have all been there. Focus your mind on other aspects of your life and force yourself not to dwell on what she is doing, what day it is for her, or anything about her at this point. I am not suggesting quit loving her. I am suggesting taking that love, stick it in a box, put it on the shelf, and go get it once you and your W are at the point you need it again. You will find by reading the success stories here, most of the ones who have the greatest success and quickest success are those who detached quickly, and to the point their spouse thought they had truly moved on. That should be your encouragement and motivation for working on this.
Best of luck to you!
Me: 42 W: 32 Married 7 years together 8.5 S1: 7 S2:7 Bomb #1: 09-16-13 Recon #1: 11/13 A discovered 04-03-2014 W filed D 05-19-14 but never served me I filed D 12-02-2014 S 05-31-14 Divorced 5-19-16