Has the RelationSHIP Sailed?

Today I started wondering, is my relationship dead?

This question haunts me. How to know if something is worth fighting for or is it time to leave the sinking ship? Like rats. It feels like giving up on something that once felt like the most important thing. Lots of water has passed under the bridge and something has happened that rocked the boat heavily. I've felt like a fool with my significant other fooling around in our relationship when I thought we were serious. He proposed. I was happy for a year, even more so when we started to really plan our wedding. And then it came. A title wave of uncertainty when I discovered something my hubby-to-be had been doing. Not a pretty thing (okay, but not the worst you can imagine).

I thought we were passed all that. In our relationship I've felt the best and clearly the worst. Is this roller coaster ride something I can be in without getting sick, mentally throwing up until there's no fur balls left to vomit? Are the good things enough to keep us together or is it time to cut the cord? Is the trust and the spark gone?

No one else can answer these questions for me. I know that. But if you have similar experiences I would be happy to hear how you've managed to continue or have you left the sinking relationSHIP. I feel like there's still a chance if we light up our fire and manage to really commit and trust each other.