I was in a dark place also. We had just moved 2 states over and my gf now future wife this week actually. Was getting ready to have our 1st kid back in 2012. I didn't really want much to do with us so I was flirting and trying to find attention else where when I was also chatting my summer fling up back home. We were basically broken up at this point and I was drinking way too much. We came back home to visit family and I went on a date with the fling after a rugby tournament...on future wife's birthday of all days. She still brings it up when we bicker but I'm way past it now. I've never been happier. Though I'm sure some can't say the same. Good luck man and I know how you feel.

But, it's better to tell her now before she finds out on her own. Just need to communicate and lay it all out on the table. Tell her what you're going through.