It seems like your main concern is whether you are an equal partner in the relationship. From your post, it sounds like you are important to m and r. They take your feelings into consideration, show you respect and care. That's wonderful.
In regards to your insecurity, I'd like to draw an analogy from my life. I have two best friends. I met one when I was five (j) and one when I was 13 (v) Today, I cannot honestly say that I love one more than another, or that one is more important than the other. I love them both as much as I am able to love. Now if you had asked me when I was 14 who I had a deeper relationship with, I probably would have said j due to the long history we had together. However, many moons later, the difference in the time I have known them makes no difference. The decade I have known v has been more than enough time to catch up with j. As the years passed after I met v, the gap became smaller and smaller until it didn't exist at all.
V didn't worry if he was equal to j for the first few years I knew him. He knew that I cared for him and did what I could to foster a deep relationship with him. He knew that if time passed and we continued to relate so well, we would become more and more important to each other. There is nobody more important to me than him today, but that wasn't the case after the first year.
When i went to college 500 miles away from v and j, I was worried our bond would suffer. In actuality, it deepened. I relied on j and v to help me make big adjustments in my life, to listen to me tell of my mistakes and still love me, to share their lives with me even when it wasn't convenient. J and v found stability long before I did, and they used that to help me through rough times. Now that the tables have turned somewhat, I use the tools available to me to help them.
It's hard and worrisome to have different life circumstances than your loves, but you can maintain a connection if you're willing to share your life with them. You need to accept that you are in a different place in your life, be open with them about what you're doing and what you're going through, and invite them to share things with you that you might not be experiencing yet. Work to keep the relationship healthy, but don't stress about the temporal issues. Know that if you're compatible, you all want an equal relationship eventually, you work hard and you're honest, your relationship with them will catch up of its own accord. If you feel one of those things isn't in place, thats the problem, not the fact that you are not in the same place right now. In 15 years who's closest to who will likely have to do with communication styles, sexual preferences, schedules and interests rather than length of relationship.
If I were you, I'd let them know you are happy that they are moving forward. Sharing the joy they bring one another will strengthen your relationship and is important. I'd also let them know about your insecurity regarding your different place in life. Chances are, they've thought about it too. If you talk openly about it and come up with ideas for how to handle it together, your chances of thriving are greater.