I was so sad reading your post. You deserve a lot better than this, and just reading what you wrote it was instantly clear what a generally good guy you are.
Here are my thoughts
I've been cheated on and lied to in just about every relationship.
Every single relationship ends. Be it in divorce, breakups or death. If /when you do end up with the person you will grow old with - you will be with them because every other relationship failed. So don't beat yourself up about things going wrong.
That said, cheating is a pretty specific behavior (as is lying), and it often comes with certain characteristics of the person doing it. Selfishness, low self esteem, craving external validation, or a variety of personality disorders. Healthy people respect and love themselves too much to cheat. So it would be good if you could think about what it is that might be attracting you to people with these broken or malignant characteristics.
It might be something in your past, it might be a knight in shining armour complex, or it might be that sometimes broken people are excellent love bombers! Maybe it would be healing to list out these relationships and look at what their flaws where and what it was that attracted you to begin with.
You might then start to see you're not a person who gets cheated on and lied to. You might instead be a person who's drawn to (for some reason), people who lie and cheat. That is their characteristic. They are a liar and a cheat. You aren't the problem.
When I started dating my significant other 4 years ago I told her about my trust issues. A few years ago I caught her cheating through snapchat. It took some time but I forgave her. In October 2022 I found out she was again talking to other guys on social media and sending/receiving photos and videos.
This shows she's not capable of empathy and real caring.
I confronted her and she ended things.
And this shows she's unremorseful about it.
I told her I was done and wanted her to move out. She begged and cried and threatened to kill herself.. "If we can't be together then there's no reason for me to be alive anymore".
I was pushed to being suicidal by my WH's infidelity. It broke me. What she is doing here though is flat out manipulation that is diverting away entirely from taking responsibility for her own shitty behavior and instead trying to use FOG. Which is:
FEAR: fear you will end up with her dead
GUILT: guilt that you are making her suicidal
OBLIGATION: the concept you have to do what she wants or face the above
This is really classic red flags for a personality disorder. Perhaps narcissism, but based on everything else you said I am calling an armchair diagnosis of Borderline Personality Disorder. Have a Google on that. She sounds like a classic case.
I kept telling her no for days and days and she wouldn't stop crying and begging. I told her I'd think about it and that she has alot of proving to do while I'm thinking. She immediately deleted all social media on her phone and she has been acting more affectionate and respectful towards me. She has also started therapy and told me she came to the conclusion that she has cheated on me on social media all those times because she was always the ugly duckling growing up and had no friends, so now she craves and is addicted to attention from others and to feel wanted from others.. which baffles me because I have always gave her constant attention and treated her like a queen.
This all correlates with borderline personality disorder. If she has that, there is nothing you can do to make her feel loved enough - she will just act out for attention and crave drama and the highs and lows. There will be an abusive and repeated cycle of bad behavior followed by remorse. Lather, rinse, repeat.
But we have a daughter together and I'm the only father her son has ever known. It's a very confusing time for me. My heart and mind are in constant battle on what to do. She has made me feel absolutely worthless and I feel like I'll never be good enough.
Everything in your message is shining proof of your worthiness. You've been kind, loyal and in the midst of this shit show you are thinking about her child. The world would be better if more people had these qualities. It sounds to me like you're done with the relationship and are trapped in an abusive cycle. This can be very hard for men to see.
Please read up on the condition. I know it's terrible to try and diagnose these things from a paragraph on the internet but it would be interesting if you read up on it and see what you think!