Stuck in the middle

So my best friend (male) recently entered a relationship with his ex, after him and his ex fiancé (became friends with her through him) decided to take a "break"....from what I've been told?. He's been messing around on his current girlfriend with his ex fiancé. I know it's "none of my business" but of course being friends with both of them I'm automatically pulled into this mix of a mess. I try to talk to him and tell him what he's doing isn't right and he needs to decide what he wants. He's told me and his ex fiancé that his heart is for her and he's still in love with her...but he cares for his new girlfriend, but doesn't see himself loving her the way he loves his ex fiancé?

Where I'm going with this is....his ex fiancé (my now, good friend) constantly asks me why he's okay with cheating on his new gf and constantly looks to me for answers. I know he loves her but I don't have the answer to this. I've told her he feels like he's stuck in a situation... and for her to be patient but to also go out an enjoy herself. Any of you glow gals have some good advice to give?

I hate being in the middle but I want them best for them and their child. I know they should be together but everything is just a mess at this point and I'm losing myself trying to help. 🤦🏾‍♀️