How many times have you texted, emailed, called, stopped by uninvited? Stop. Just Stop.
You're in a world of hurt, looking for validation. And you're dealing with other people in a world of hurt not knowing which way is up.
The more you pursue your stepchildren, the more they'll believe what their mom says about you stalking her.
Let. It. Go.
Your relationship with your spouse has not been an ideal for quite a while. Neither was mine, but I felt at the core it was. It wasn't. Like Humpty Dumpty after the great fall, no amount of work could put it together again.
Reality hurts. It really really does.
But clinging onto the dream is worse.
That horse is dead. That ship has sailed and sunk.
Just Stop.
Stop all communication with your stepchildren. Limit any communication with your divorcing spouse.
Set your boundaries.
The stepchildren will reconnect with your son. In time they may reconnect with you.
Let them come to you. Stop pursuing.
And if they don't, you know what you gave unconditionally.