Hi Abbey- I've been out of touch for awhile, just caught up on your last few pages of posts. Your much deserved venting set aside, your posts are mostly about what he is doing and your efforts to track what he is up to.
My tentative advice to you....save up some cash and hire a private investigator. Document the affair so that you don't feel crazy any more. Then decide what you are going to do. I'm not advocating divorce or confrontation or any other specifics. But you are in control of your life and I want you to stop chasing him around letting him mess with your head like this. Take back the power you have over your life. I do think you need to know for sure and be able to prove he is cheating - it sounds like you're getting close to the edge of what you're going to tolerate from him without blowing up and confronting him. If you want to, do a free consultation with a local attorney to find out what lies ahead if this does blow up. It would be for you to know your options, not to shake things up - don't let anyone rile you up or push you away from DBing or the path you want to take.
Regardless of what you decide, you should have a solid financial plan in place, in case this does end in divorce after your kids are both in college (very soon, right?), you should make sure you have copies of financial records/account numbers/tax returns in a safe place, you should ensure that you have some money in an account he cannot access so that you can function for a couple months.
I don't know what more experienced DBers would have to say to that....I just feel thing overwhelming sense that maybe you're going down cheeseless tunnels and he's not responding and you're getting worn down and just going along with it, rather than chosing to detach and chosing to wage war against the infidelity. Lots of love and all my best to you. I still believe you can come back to a good marriage and happiness.
It sounds like he is doing more things with you, which is great. It bothers me a lot that he threw your bday card away. Very petty and mean. Keep focusing on those positive interations with him and keep taking your time away from him. Good for you, going to the gym and on hikes and all these fun things.
Faith is, at one and the same time, absolutely necessary and altogether impossible. --Stanislaw Lem