I understand this sentiment for sure, and I don't necessarily disagree with it, but it seems like an extra 3 months doing everything to make it work wouldn't be the worse thing in the world.
I can respect you giving it 3 more months to try and work things out. I think you can also work on improving yourself over that time. Women are 1000 times better than guys in end of the relationship situations. A woman in your situation would either have the next dude picked out or would at least be taking huge self improvement steps. A lot of the guys I know in your situation know it's coming, but don't do anything about it and end up depressed and mopey right after it ends. Here's what I'll do after my next big breakup.
1. Go see a divorce lawyer now. For all you know, walking into his office gives you new perspective and really makes you work to stick it out over the next few months. Or it might do the opposite.
2. Start getting into shape. Do P90x. Start going to the gym and lifting. Start taking BJJ classes. Whatever. Find something that works for you. In any scenario, having some physical activity is going to increase your happiness and overall mental health. You're going through a difficult time, and you deserve to get better.
3. Pick up some hobbies outside of work and your wife. This certainly goes hand-in-hand with the above. Bird watching, yoga, rock climbing, martial arts, stamp collecting. It doesn't matter. Spend some time on yourself.
4.. Pick up a decent camera. You can either buy one or borrow one. Get some good pictures of yourself. You want a few of you looking hot as ####. Anyone looks good if you take enough photos. Your confidence is going to go up just by seeing yourself look great. You want a few more of you doing cool stuff. Go skydiving. They take your picture during the jump. The goal is to get some pictures that you might use later, but in the mean time you're jumping out of airplanes or skiing or hiking or whatever.
If you fix your marriage in the next 90 days, this is all just gravy. If your marriage does not work out, you download Tinder and Bumble. You've got killer pictures of you looking great and doing cool #### that are high quality. Making the out of focus cell phone selfies and sad, desperate profiles that you're competing against look awful in comparison. Either way you're in shape, you've picked up new activities that are enjoyable, and you've had life experiences that you otherwise wouldn't.