I think Tom and Diana should have gotten married
At least then when Tom has another heart attack, Diana won't have so much difficulty like she did in the first season and the same thing with Tom if something happens to Diana. And hey! Who says that getting married changes anything other then their titles or that they share each other's things or not?
I always said that I would only get married after I have done everything I have always wanted to do and be older and wiser and so on like Diana.