I F27 have been with my partner M29 for 10 years

Having a family has always been something we have talked about however recently he seems unsure on having children. Also we’re due to marry last June but he freaked out and said it was all getting too much so I cancelled it. On paper this sounds awful, but we really do get along so well and are happy- hence the ten years together, but it seems our life goals aren’t adding up. I think I just need help to justify leaving as I feel like I would be the one ruining what we have, when what we have is perfect for him. I’m thinking if he can’t decide on children and backs out of marriage, my only choice is to leave?