I'll try to keep it short. Basically, my friend has had an on-off relationship with the mother of his children for a few years. I have never met her, we are former colleagues and have kept in touch over facebook, the odd coffee or lending books to eachother etc.
I guess we have very unique similar interests, so we don't have anyone else we know that have any of the same hobbies, not even my OH (who thinks I'm a massive geek and is thankful to friend for keeping it out of his earshot 
) which means that we talk a fair bit. We get on really well.
Recently, he's back on with his ex. And she's told him that she isn't happy with him talking to me, and that she's always suspected that my friend may have feelings for me. She's asked him to cut me out of his life, basically.
I'm shocked, and a bit upset. But I understand. I've tried to imagine it from her point of view, their relationship is unsteady, and she has reason to not fully trust him around other women. He slept with one of our colleagues when they were broken up... I think in her position I'd be wary too. He's told me he's not going to stop speaking to me, and that she's being unreasonable.
Is this any of my business? No. But has he told me anyway? Yes. So I feel kind of responsible for her feelings, being that our friendship seems to be causing her pain. So, would it be best to back off despite his insistence that he doesn't want me to? I don't know.
Tell me to move this to relationships if it's misplaced, I thought I could get some good answers from you guys.