I'm glad you're approaching this as pragmatically as possible. Definitely don't be afraid to ask for more time or more affection. This all has to balance. If there's no balance, then it will fall apart. This is where a lot of poly relationships fail... make this work by telling him what your needs and requirements are. That's not unfair, that's working out the issues before they become problems.

Poly literature is just that... they are promoting the lifestyle from a perspective that this is the most perfect way a person can love. Yes, it sets you free, gives you more support, helps you meet more of your needs, and gives you more love back than you can ever imagine. However, there IS jealousy and fear. Every seminar or book addresses this in some form or another. Human nature is to fear what's new or different. Eventually, we usually discover what we feared is now something to relish. Don't let your feelings of fear make you feel like there is something is wrong with you. I'm telling you that I've seen it many times (friends and us). Eventually, it smooths out one way or the other. Often, the NRE wears off and the relationship settles down or disintegrates and life goes back to how it was before. What I see most commonly is that the Metas become part of the family.

My wife did have a GF. Because of the other woman's insecurities it didn't work out. I was happy for them when they were dating because they were so cute together and made each other happy.

Currently, my wife and I are both dating the same woman, which makes things a little easier. We've essentially closed our triad and are happy with the family we have created. Our GF has a husband who is not romantically involved but we all love him very much and their kids are our kids and vice versa. "One Family" is what we say.

One thing I will say. If their relationship is as fast and furious as you say, interfering in it will explode in your face. Tell him what YOU need, but try not to limit their relationship except for the time you and your family need. Don't be afraid to tell him what you need.