He was kicked out or left, I'm not sure which, about 18 years ago and in between his had 2 kids out of wedlock by 2 women, been to jail and has battled with addiction prior to meeting me.
People who are raised as JW's and then leave while they are quite young or leave because they were disfellowshipped, often still carry around the wrong idea that JW's are the only true religion and they view themselves as wicked and or lost causes. Because of this they often go down a road of self-destructive behavior and stay on it until they either return to the JW's or they fully and completely come to realize that the religion wasn't true in the first place. In cases where they do return, it usually isn't permanent. Usually the same issues that caused them to leave in the first-place, come up again. Hopefully this takes place before they've compounded the problem by getting someone else involved such as a new JW spouse or a child.
People change and I believe in forgiveness but in view of the past issues this fellow has had in the recent past, coupled with this sudden change that has taken place, as difficult as it may be at first, I'd say you are fortunate to have had this happen now rather than later.
I don't believe God (if he exists) intervenes in our love lives, he likely has a lot more on his plate these days, but if you do think he is somehow involved, why wouldn't it be because he is trying to protect you and your children rather than to cause you heartache?
Your friend has been clean and sober for a little over a year and it's likely that because he no longer has a crutch to lean on, he has chosen a religion that makes him feel safe and left you and your children hanging. It sounds as if he ended the relationship and didn't offer you any choice in the matter.
I hope things work out for him and that you can eventually take pity on the miserable person he must be at this point. In the meantime, I'd say your instincts to put your kids first, is spot on. It's obviously too soon to hitch your wagon to someone who has had and is having the kinds of issues this man has.