<human>: So the description says it all mostly.

Backstory;

I was married to my ex for 3 years, and divorced bc I found out he was cheating on me. We have a little girl who is 6 years old now. We have been divorced for about 3 years. 

Him and I have always tried to remain friends, because although he might be a bad husband he was never a bad Dad. Back this past February he hung out with me and one of my best friends. After we all got done hanging out he told me he thought she was cute, I told her, she said she thought he was cute as well but "he is you're ex and your baby daddy so I can't really do much about it".  Me, trying to be the better person, because I am in a happy relationship said "hey whatever, who am I to disrupt happiness" and told them that they could go on a date.

I never really expected either of them to go for it, but they did, and I know that's my fault for telling them that it's ok.  We had extensive talks about it, both with the best friend and the ex-husband, both promised nothing would get weird and nothing would get  in the way of friendship.

Everything was great for a while, her and I continued friendship and she was a big help with getting my daughter ready for school.  He continued to be a good Dad and we (me, my boyfriend, best friend, ex husband) all managed to hang out and have drinks a couple times.

Well, guess what?! SURPRISE! SUPRISE! Shit got weird! My ex-husband has been lax on paying child support and with helping out in general.  I haven't talked to my "best friend" in 3 weeks (we used to talk at least twice a week and text several times a day).

I miss her, but things have obviously changed. I know it's my fault, am I best to cut my losses and move on??

(Sorry if this is wrong subreddit, trying my best here)

Can you give me a shortened version of the text?
<bot>: My best friend and ex-husband (and baby daddy) are dating, have been for months after my permission, things have just started to get weird... What do I do??