Kaya, he can only pull the rug out from under you if you're standing on it. You've made a great start by going non-contact, and you know from experience how it's going to proceed. He's going to bombard you (via your F&F) with love, apologies, explanations. Why not? It's worked before. I bet if you sat down with his ex-wife you'd hear some stories that would shock you and yet sound familiar.
You've got away, now keep going. I know it's hard to step away from your 'best friend' but you have ample evidence that he's using you. You assert yourself in any way and he turns on you.
The text message was truer than you think - help with the kids, a warm body, money..... I know it hurts because you gave away a part of yourself to this selfish A, but there's no future with him.