> "I hope to heaven that the startup never ruins my marriage but it's not impossible to see it could happen"

I know it's (way) easier said than done, but I would suggets to stop hoping and start doing. I have never been married nor in a big commitment relationship, but I would assume than when you start thinking that a bad thing could happen, it's probably happening right now, or soon.

Good luck anyway, hope everything work out for you.