Just a few words of personal experience on this...
My boyfriend, sister and best friend all work for for cruise liners and I'm sorry to say that as a general rule they are just not interested in hooking up with passengers or keeping in contact after you leave. What you have to remember is this is a short holiday for you where you meet new people briefly then go home. For them this is every day life and as quickly as you come and go, a new boat load of people come on and it stop, starts all over again. They meet at least 2000 new people every single week, so as unique and special as you think you are to them or that you think your connection was, generally for them it's just part of the job. They are paid to get the passengers to feel special and they are rated according to how many compliments, recommendations, or complaints that they get from passengers - this then affects their future pay rates and job advancements. So of course they will flirt and smile and make you feel like a million bucks, it's in their best interests! Because of this, they are AAAAALWAYS getting numbers and emails and facebook messages from enamoured passengers (trust me, we often joke about it) and it's rare, if ever, that they keep in contact back. Plus you have to remember they work HARD, sometimes 16-20 hours every day depending on the company so even if you give them your contact details, they don't really have the time to pop on down to port, find an internet connection and start chatting to or emailing passengers, however nice they were. Any little free time is spent eating, sleeping and snatching precious moments to talk to family and loved ones whom they haven't seen for months. Also, this is their normal life remember, so they almost always have a partner on board with them or a family back home they are saving money for because they can earn a better wage working in the ship. I'm not trying too burst anyone's bubble here, but just telling it like it is, speaking from years and years of personal experience.
As a disclaimer, I have to admit, I did meet my boyfriend on a cruise ship, but my entire family was visiting my sister and they are friends and worked together. So for the two weeks we were on board we were often all down in the crew areas (special permissions) or up in our cabins. He then came to visit our family at the end of the contract and stayed with me as a result. So whilst technically we met on a cruise, the circumstances were pretty different. I've done a number of other cruises before and after and the reality I posted above has always been the case.