Hindsight is a curse gift that we all possess, but it's our lack of foresight that causes most of our problems.
Were you so complacent that you thought he'd dance attendance on you forever while you spurned his advances? If so, you need to learn that playing power games inevitably results in a winner and, if you make gross errors of judgement, it won't always be you that emerges victorious.
The more you beg and plead at this point in time while he's loved up with the new woman in his life, the more chance there is he won''t believe that your uncannily coincidental realisation of what he means to you is genuine and if you keep it up he'll grow to despise you for the manipulative drama queen he'll believe you to be.
Let him go with good grace; wish him all the happiness in the world, be welcoming but not overly so when he calls to see/collect the dc and, as Montane has advised, DON'T be tempted to use them as a means of emotionally blackmailing or guilt-tripping him into reconciliation with you otherwise you'll soon grow tired of him again and will look for more means of relieving your boredom.
If you truly love and care for him, you'll put your fears aside and put your trust in the universe to act for the greater good of all concerned.
Whatever will be, will be and, if it's meant to happen, it'll happen without any scheming, plotting, weeping, or wailing on your part.