I advise working on accepting that what is, is. Pema Chodron writes quite a bit about that (not necessarily pertinent to poly-but definitely would fit the circumstances anyway).
As Nyc said-each individual relationship is separate and comes when it comes, is built (or not) as the participants build it.
Your "other perfect ones" may not yet have entered your life-or maybe they have and you or they just aren't yet at the point to admit/acknowledge it.
At any rate I also second Nyc's opinion that you should rejoice in it going one at a time. Every new relationship brings change and complication that must be managed. So having them happen separately (the start-ups) makes life much smoother to manage.
Pamper yourself. Make a list of things you've always wanted to do (like a bucket list) that your partner has little or no interest in. Then, schedule to start doing them while she's busy with her new partner.
It will keep you busy doing something YOU WANT to do & it very well may lead to you meeting the next person who you fall madly interested in.