I’m about to be after 15 or so years but the reasons I said “No” in the past have been.
1. Partner didn’t want to wait on the relationship to age a bit, I said he should be 25yrs old minimum. My thoughts were wanting to give him time to mature, experience more exposure to adults, make sure I was “The One” and not to settle just because I was good to him.
2. Partner was a psychopath and I couldn’t wait to escape. The proposal just made me more frantic.
3. I’d married one best friend already and knew I wouldn’t do well by marrying another best friend.
4. The relationship I thought was so magnificent got derailed when my partner expressed how much he hated my job that was supporting us. I looked at him and realized he was happy with his life/jobs as they were and I wasn’t and wouldn’t be if I remained. I wanted someone similarly ambitious and suddenly felt alone and awkward.
5. I realized loved wasn’t enough to overcome another person’s anger, depression, lost dreams and the proposal would have sealed my fate to become as miserable as that person.
6. A proposal for someone to take care of me, take care of my mother and basically restore anything I’d ever lost in my life (material stuff) was turned down because the idea of security, financially comfort and love on that person’s part wasn’t enough to spark love in my heart.