Advice before getting married

Me and my boyfriend been together for 7 years now , we got 3 beautiful kids together, we always talked about getting married but we don’t want to rush, but I feel like after our 3rd we should be ready to tie the knot, but he seems like he not ready. I’m starting to feel like I might not be the right person for him. Should I just wait and see or should I just say we can see other people?