You want to make sure that everything is completely his choice, but let him know that he doesn’t have to transition. If he feels he is a man that doesn’t mean that he has to transition. There are plenty of ftm transmen that do not transition. There are a lot of confusing feelings going on with both of you. This can be so new for both of you and what is really important is communicating with one another. Making feelings very clear and make sure to ask him what he wants you to call him and what he wants. Assure him that you love him often and make sure you are always there for him. (:
I hope I could help!