I'm in love with my best friend...

So, for the last 3 years me and my "best friend" have been fooling around with each other. I've slept with him so many times it will make your head spin, in the non sexual way. so I don't know what to do when I get told that he is going on a date tonight with his ex girlfriend. Who put him in the worst position ever by having her and her children move in with him and then out of nowhere stays with him for two weeks and then she packed her stuff up and moved back in with her ex boyfriend. leaving him crushed and destroyed, and I had to help pick up the pieces and make him feel better again. now I get told that him and her are going on a date tonight, because he wants to talk to her about what she did to him and what his feelings are. Telling me that he still has feelings for her and wants to take care of her. Tell her what she missed out on by running out on him. Say the things that he feels.The thing is she hasn't responded responded to him in almost 5 or 6 months and now that he has a good job and makes about a thousand dollars a week. She comes back in the picture after seeinf him post something on fb about an 948.00 check for one week. I think "know" it's just to use him and have him take care of her plus her kids, because she's just a drug addict heroin and pills injects and single mother too. her xboyfriend is a drug dealer. Its just not right and I don't know what to do because its killing me inside, Because HE IS THE ONLY PERSON I'VE EVER HAD FEELINGS FOR, LIKE SERIOUS I'M IN LOVE WITH HIM FEELINGS. but I don't want to be a bad friend and not support his decisions, but I just think he's getting used for the money now that she and her ex boyfriend are not together and is broke and he is not especially when he works for a company that picks fields like corn and lima beans where he's gone for weeks at a time so she can just do whatever she wants and stay at his house for free with her kids and just talked to him on the phone after a 12 hour shift. so am I wrong here to tell him that he's not in the right space and right state of mind to do this? if she's just trying to get him back just to use him again for a place to stay and have her be taken care of again? He's "straight" and I'm out gay... been friends our whole lives and started fooling around 3 years ago now. Going on 4 on my birthday next month.... SERIOUSLY I NEED ADVICE