Grab your cups of tea this might be a long one but I really need some guidance on this!!! Please help where you can!!!

So I have been with current boyfriend for nearly 3 years, I met him through my best friend(sort of ex best friend) things got complicated when me and him officially got together! It’s her brother by the way! I’ve know his family for at least 7 years and have always basically been part of the family even before me and him were together! He has a child who turned 5 a few months ago! She’s(the little girl)known me all her life as I was friends with his sister when she was born (his ex is the mother of the girl). When me and him started speaking I feel like I’m the back of my mind I knew it wasn’t right to do it when my friend didn’t like it, we all do things wrong sometimes and it was something new and exciting so I carried on talking to him! Me and my friend( Emily - fake name) had a few fall outs where Emily said she didn’t want to speak to me anymore and she couldn’t be friends cause it’s too hard she’s going to lose her best friend! Anyway we get on now I think because we have to and cause we see each other often, but I don’t think she classes me as a true friend anymore!!! Me and him have been great we practically never have disagreements and are always on good terms! He bugs me sometimes as I think he’s got lazy but who doesn’t when they get comfortable in a relationship!? We’re all guilty of it! But recently I keep thinking to my self about breaking up with him. It I have no reason to!? Literally no reason to? I don’t know why I keep getting this thought in my head when we are as good as we have always been!? We have been joking about recently about engagement rings and stuff as one of my other cousins recently got engaged but when I sit and think I feel I don’t see my self walking down the isle with him? Is that wrong? His family means the world to me his daughter I treat as I would treat my own! His family are great i love them all( I’m crying as I write this)and I’ve known them for SO long! He doesn’t really go out anywhere only with me / his family so I thought where would he meet anyone else? I want him to be happy! He love me and I do love him! I just don’t see my self walking down the Isle to him at the end!? Again I have no reason to be thinking about breaking up? So why does this though come back to me every few day?????? Please help!?! I don’t want to lose a best friend and a boy friend and a great family for no reason!? I have no reason to break up with him? It just doesn’t make sense? Is this a gut feeling?