Being FTM (as am I) is much more than a decision to change. Imagine that you woke up tomorrow morning and your breasts are gone, your body was covered in hair, and you had other noticeable changes to your *aherm* lower regions. You would freak out, wouldn't you? You would want to know what happened and where your body went, right? Being transgender is just like that EVERY SINGLE DAY. The emotional impact of being stuck in the wrong body, and nobody understanding, is a huge one. I fought tooth and nail to get my parents to understand that, despite my physical attributes, that I was a guy! My mother forced me into frilly dresses, and forbid me from taking shop class and playing football. I was stuck doing proper "girl" things such as home economics. It's hard, because NOBODY understands transgenders. Just like being gay 50 years ago was taboo, today being trans is taboo. It makes transitioning very hard. Dating for transgendered people is VERY HARD. Can you imagine walking up to a girl in a club and really hitting it off, only to find out that that cute girl you've been hitting on all night isn't really a girl? I think that's why transmen have such trouble dating lesbians. Think about all the surgeries that a transman must go through. All the torturous years of self-hate and social outcast for being nothing more than who you truly are... Then they find out that now, when they've finally become the man they were supposed to be all along, they're being hit on by someone who, in general, only hits on chicks. The last thing you want is to go through all that pain, just to think that you're still girly in any way. You'll find that a lot of transmen kind of... overplay their manliness because of this. If you want to hit it off with this guy, treat him like A GUY. Try and avoid using the word lesbian, or perhaps say that you're bi instead... It'll make him more comfortable, and you won't have any awkward explaining to do...
I hope all goes well for you, and I apologize for the long rambling shpeal, but I hoped that it helped in some small way...