HELP!?!?!? SEX TROUBLE!!

I love my boyfriend a lot.., we’ve been through so much together and I can’t imagine a life without him, however, I’ve noticed that I just keep getting bored and sad when I’m with him and sex isn’t the same anymore... sometimes we have good sex but it isn’t ever really enough for me I guess? I don’t really know how to tell him that though... I don’t wanna hurt his feelings. I know I want to be with him and have a future together but things are changing and idk why:/ any suggestions??