need some advice please.. sorry its long..

so I have been with my guy for 5 years. a little back ground on us. we have been friend all our lives. were there for each other when we were married and had kids, and those fell apart. so fast forward some how we decided friend with benefits would be okay. both of us had just got out of a nasty relationship. well that turned into more. here we are 5 years later. all we do is fight. which is mainly due to his 14yr old treating everyone like trash, which she learned from her bio mom . which is a druggy and drops this kid from her life for years at a time for her next high or worthless guy. anyways. he won't see it. the last year I started talking to a joint friend of ours. he trys to be supportive to both sides. well they work together and I guess my guy has been trash talking me at work. saying I'm cheating and telling our joint friend all kinds of crap. mind you he is saying crap in front of many people who know both of us and over the radio so everyone hears it. in my defense I am home most of the time with the 14yr old and our 4 yr old. when I'm not home I'm in class trying to get my degree or I have the kids with me. he has gone throw my phone. asked me to stop talking to my best friend which I have. I even deactivated my fb. but nothing is good enough. anyways our joint friend out of the blue kissed me. at first I was shocked but my God to be kissed with such passion and told I'm amazing in every way possible, felt really good. however my brain kicked in and I pushed him away. what should I do. if I tell my guy what happen he will freak and say I cheated. it only happened the one time. our joint friend and I still talk but keep a distance we all BBQ together and hang out. I just don't know what to do. I love him but, I can't handle being treated like shit by his daughter and him. we have an amazing 4yr old together. what do I do.....