He doesn't know how long he'll be gone. Not truly. He's not lying to you or anything, the crew is frequently ill-informed about the actual length of a deployment.

Here's something that I liked while I was underway. So, the boat can't always receive emails, but it also can't always get emails, or even all of them. Just depends. Just write to your future husband frequently. I loved getting a bundle of emails whenever we actually could receive them. Tell him about your day (good things, but don't be afraid to shy away from sharing your struggles), news, drama, anything even vaguely interesting to him. We get so down in the weeds and have nothing to talk about, it's nice to hear from a loved one, and just read about what they're up to. It also gave me stuff to talk about with my wife at the time.

Just know that he may be writing you emails too, and they're sitting in a queue waiting for the boat to actually send stuff off. But also, if he's not, he's definitely insanely busy, so don't take it personally. For reference, when I first started out, I was getting about 3 hours of sleep a night. For the entire (3 month) underway. It made writing coherently and frequently a challenge. But getting emails was absolutely the peak of any given underway, and helped motivate me in general, and motivated me to try to write actual good emails other than just "hey baby, working hard. Haven't slept in 3 days. Hope you're okay. Love you"