Are there any success stories about that, or ideas where to start ?
They were two of the smartest people that I have met in my business ventures. What I loved is that they each recognized and honored their partner's strengths. Peter was very strong technically and Kate was the business strategist, sales, marketing and deal maker. And, to my eyes they seemed deeply in love and still enjoyed spending time together.
We almost found a way to do business together but they were at a different phase in life. They were getting ready to sell their second business and were psychologically getting ready to move money into more stable investments rather than another start-up.
As Peter and Kate demonstrated it can work wonderfully to mix business and personal relationships. However, most people find that the combination is just too stressful. I love my wife but have no sense that we could be a Peter and Kate.
My advice is that if you do work together you need to make sure that each partner brings something to the business that is vital, is in their competency zone and that they enjoy doing.