We sat at a table towards the back of the establishment. He pulled out his laptop and began coding furiously, intense concentration etched on his face. Now was not the time to interrupt or make chit-chat.
To be in a relationship with someone heavily involved in a start-up, you need to put aside the "me" and focus on being a partner. Look towards the future and make the present, well, pleasant. There's no room for bullshit. If you're insecure, unhappy that you're not getting to do what you want, slighted that the focus isn't on you, it's not going to work. Although all relationships should be partnerships, the added strain of late nights, early mornings, and heavy workloads really puts them to the test.
One of the best ways to combat this is to get involved yourself.
I'd add that if you're the founder, rather than the SO, the reverse of this is true: get your partner involved. Drag them along so they're as excited about things as you are.