My Best Girlfriend's Man's Flirting with Me......... what to do?

My best girlfriend’s partner is flirting with me whenever we get together. He’s lot older than me, and seems quite happy living with my girlfriend. About a year ago, when we were alone by ourselves in a hotel room, he has been very playful, he tickled me from the couch to the floor, as I got flushed I knew I have to leave the room to cool off, or something will happen between us. As I was leaving the room, he tried to stop me, and hug me, eventually I left the room, just, be honest, I quite like him, maybe even enjoy the sensual tension. I am married for 9 years with a young kid. My relationship with my husband is not going too well at the moment. At times I was thinking about leaving. The feeling I have towards to my best friend’s partner is still strong, even though nothing has happened. And last weekend when our families were catching up, he was flirting with me. I don’t think I will leave my husband because of him. But what do you think of his intention? I don’t want to lose my best friend. He’s aware of the trouble that I am having with my husband. He seduced me even more that day, what’s going on here?! I like him being flirty, but I don’t think now is the right time. But to say that, the thought of having him close to me just drives me crazy. Can you help me analise the situation please? I am so confused.