I think Andrea is faithful and running long term relationship according to his track record. When he was seeing Carolina Von Stauffenberg, it went on for quite a long time. Something must went wrong with them, not necessary whose mistake, just could simply be they were not right for each other. They two were from quite similar background and involved with a certain group of people. As age grows up, Andrea, the freedom yearning man would want to break the frame for something his soul wants.
It was certainly a bridge relationship with that Spanish actress. She caught his eyes as she is different but she doesn't possess the attributes he is looking for. As soon as he realised that he left. The relationship even didn't last 2 months, didn't it? Maybe 'relationship' itself is a wrong word.
Tati's family is wealthy, but she is a commoner. She is brought up in the way that a commoner would be with more money, of course, a lot more money
. However, she is not vain. I don't feel she fancies a royal boyfriend to add a gloria, which a lot of royal-commoner relationship is tinted with. She simply loves him. They stroll down the market, having ice-cream in the street. That's exactly the life Andrea is looking for and he gets it. I don't dare to say how long the relationship will go, but if, just if, they broke up, I would feel sad.