Time to break up?

How do you know it’s time to end your relationship? With my first boyfriend who I’ve been with for a few years now but recently feel like when I’m with him it’s like being with a friend and that I don’t feel attracted to him in the same way. Have mentioned it to him but said I didn’t want to act on it in case it was just a phase - however things don’t seem to be changing. I still love him very much and care about him a lot but I don’t know what to do because I’m scared I’ll make the wrong decision. Do you guys have any advice or have had similar experiences?