I agree with ShrodingersCat. You shouldn't need to worry about sounding jealous. You shouldn't even need to worry about being jealous. It is ok to feel a little jealous sometimes. Why are you worried about that? Do you feel that if you try to talk to him, he will just dismiss you by saying "you're just jealous"? If that happens, it's not cool and you need to tell him that. He is your partner, and he can help you by listening to your worries, and alleviating your fears, and he should be willing to do that. We all need a bit of support every now and then.
Originally Posted by amdada
I don't want to control how much time they spend together, but at the same time, I wonder if they are getting too caught up in the NRE and setting themselves up for hurt later, when someone finds a new partner, or gets a time consuming job, or moves closer to me...etc. I have tried to talk to my partner about it but don't know how to approach the subject without sounding jealous.
Think about what people are like when they are in NRE in mono relationships. They tend to spend time with each other 24/7. Whether mono or poly, it's ok as long as existing commitments aren't ignored too badly (in poly the existing commitments just include existing partner(s)). You don't need to worry about them being hurt when they can't spend all that time with each other anymore. They'll be fine and get used to it when the time comes, and besides NRE passes in a while and they'll be themselves again.
Now then, on to you. If you feel that your partner is giving you the same attention and consideration now that he was before, that's good. However, if you feel like he isn't, or even if you feel that you need a little more to help you feel like he isn't forgetting you, you should communicate that to him. If you feel like you'd like a bit more from him, try to think about something concrete to ask for. It's can be hard to respond to a abstract wish "I'd like more", easier to negotiate something when you have something to start from like "could you call me once more during week and maybe I could meet her the next time I'm there". (I don't know if you've met, but if you haven't I think that might be a good idea.)
You could also tell him that you'd like to know that he'll still have time and a place for you in his life, as he develops a relationship with her. I sense that's something you're a bit worried about? It's ok to ask him to confirm that.