Fucking my ex boyfriends best friend

Basically I just got out of a relationship and DEFINITELY NOT LOOKING FOR ONE AFTER THAT ONE so I went to smoke with a friend (ex boyfriends best friend) and after we made out and today we hung out again and ofc made out since I don’t want a relationship we were just thinking about being fuck buddys but I put him in such a uncomfortable situation... I mean my ex is his best friend he really hasn’t said anything about it. But my relationship with his friend was toxic and I opened up to him a LOT and he has my back through everything now and basically kind of dumped him as a friend because of how poor he treated me. Give me your honest opinion on this and tell me maybe what I should say or do.