Yes, me too.
I'm older than you all. I have spent my entire life looking for my 'forever' man. Every time I think I have found him, it lasts a while then ends. Then I meet a new man and think that HE must be 'the one' I've been waiting for, and the cycle starts all over again.
I've invested so much, too much, over decades,and tried so, so hard to make each relationship work. Countless hours listening to their issues, being understanding, tolerant, forgiving, learning their likes and dislikes, thinking up special treats and surprises for birthdays etc and "keeping things interesting". No matter how well it started, after 3 to 5 years each one ended: either he left me (always for someone else) or I left him after he mistreated me.
As I got older I got more desperate and my standards dropped so I would tolerate more red flags and turn a blind eye to things about him I did not like. I became more passive, less challenging, even more understanding, tolerant, devoted, sympathetic, etc.
The result was that I unwittingly fell into the hands of a covert narcissist who emotionally abused me and repeatedly triangulated me with other women, making us compete for him. I found myself in tears every day, calling the Samaritans time and again. I had to reach very deep to find the strength to dump him.
I know now that I am better off on my own. I am so much happier and calmer and no longer doing the humiliating "please don't leave me" dance. I also feel totally secure.
My experience is different from yours, OP, but look at it this way: at least you haven't been dragged time and again through the traumatic cycle of getting up false hopes, falling in love, striving to make it work, and feeling gutted time and again when it fails and then grieving and being left heart broken, only to end up alone at 55 anyway.