I don't know, after my first two relationships ended partly due to my food issues, I keep quiet about it. It's just too much for them to handle.
You know what's coming next: you are going to start bingeing, bingeing, bingeing. And since you're in the weight loss state of mind, you'll compensate by purging.
I have very carefree, non-serious relationships now, so I don't think it's important to open up to my "boyfriends" now, but this guy is your future husband. If you don't tell him you're struggling, how is he supposed to help you through it? It's always been my dream to have someone beside me when I go through tough times. You're lucky, so don't keep quiet. It also isn't fair to him. You don't want to enter into a marriage with a secret.
And as a side note, the majority of bulimics have anorexic type behavior (the severe restricting), but it's not a common progression from bulimic to anorexic. It happens, but I wouldn't worry about "becoming" anorexic. The bingeing/purging feelings keep the cycle going, and those feelings are hard to substitute with the feelings of prolonged starvation. I'm sure you're familiar with the cycle. If you don't start healthy eating now, you're setting yourself up for a massive binge. I don't have to tell you that, though. You already know.