Welcome! Some quick thoughts...
Is this guy a shared boyfriend? Such triads, where a new partner joins an existing couple, are notoriously difficult, especially for people who are new to poly and haven't yet had to deal with the inevitable issues of communication, jealousy, etc. that multiple love relationships tend to bring up. I don't say this to discourage you from pursuing this relationship, but rather to encourage you to do a lot of reading, writing, thinking, and talking, and to assume that there will be bumps in the road so that they don't blindside you.
Let me recommend especially this article (meant for people in the new guy's position): http://www.morethantwo.com/coupledating.html
You may also get good stuff by doing a tag search here for unicorn, triad, and similar topics.
One thing I will discourage you from, actually... having a new partner move in too quickly has been the downfall of many poly relationships... be careful about this! Once you're sure you've got the dynamics between the three of you all worked out it may be a perfect choice, but a few months, when you're still in the giddy new love phase, is probably not enough time for that. You don't want the issues and conflicts to come to light only after you're already all living in the same space where every issue will be magnified and no one will be able to get away to take a little space if they need to.
I hope I don't seem too critical, I truly wish you guys the best!