Welcome! I look forward to hearing more of your story, I'm sure the community will be happy to advise when you're ready to ask questions.
A quick thought. It's ok to not be emotionally available to people outside your primary relationship. If you really are "monoamorous", then it's best to just say so up front. However, if it's just about not being comfortable with the idea, in other words if it's just too scary, you may want to reconsider you approach to things. Many people *are* capable of loving more than one person at once, and you may well be one of them... it can be very hard to tell without some experiences to draw from... and if you are such a person, then feelings will likely crop up when you least expect them to whether you like it or not. But it certainly doesn't have to be a bad thing.
Most people find that, after some initial bumps, loving others doesn't take away from their primary relationship as long as it's in a context of honesty and respect. You may also just not know yet if one or both of you has the inclination and ability to love others. The important thing to do, if you're interested in continuing down this road, is to stay flexible, not put any expectations on anyone, and let each relationship take the shape its trying to take.
This may be a great read for you guys and Sabina: http://www.morethantwo.com/coupledating.html