You try and do your best. I think living together helps so that you can try to time box time together more easily. I did it along with having a first child with my S/O and it was incredibly difficult all around. A year after ultimately closing up shop after two years of work we are still dealing with leftover stuff from the startup.<p>Make sure your S/O is onboard. If it is a serious relationship you owe it to them. If they are not you have some hard choices to make.
Broad strokes - same as any other thing in a relationship - set expectations, set boundaries, over communicate, show appreciation, set daily / weekly / monthly catch-ups, set aside some non-flexible together time.<p>Specific to startups / starting a company, have a series of serious conversations about:<p>1. how much money you are going to set aside to get it to work<p>2. work life balance during the week, during the weekend, during "evening hours"<p>3. go / no go decision points (funding decisions, customer road map, founder / employee relationships)<p>4. social life<p>5. how much they want to be part of the company (as you will be living it, they'll be there to listen, but do they really want to listen 24/7/365?)<p>6. your goals, their goals, your goals together and how they match up with your goals for the company.
You are probably accustomed to scheduling your time carefully. If you aren't, you should be.<p>Your relationship is just as important (probably more so) as everything else, so give it space on your calendar. You can afford to take an hour to make dinner for your partner. Plan the rest of your work around it, even if you have to do so days ahead of time. Once dinner is ready, leave your phone in the other room.<p>If Obama can make time for dinner then you can too[1].<p>Most importantly: remember to thank your partner for picking up the slack so resentment doesn't build.<p>[1] <a href="https://hbr.org/2014/03/if-president-obama-can-get-home-for-dinner-why-cant-you" rel="nofollow">https://hbr.org/2014/03/if-president-obama-can-get-home-for-...</a>