@Apple7456
Why are you here?
Let's break down what you're really doing here. You're not here for advice, you're here to find people to tell you to stay with him. Because despite nearly everyone telling you to leave him all you've done is disagree and argue against that idea.
But you know deep down inside somethings not right about staying with him, but you want to ignore that part.
You're in turmoil over this, that is its own warning sign. This man has placed you in turmoil over this relationship. That's not how good relationships should go.
Apologies.
Want to know the key to an apology? Action. The words "I'm sorry" hold zero value unless there is a clear desire to change and actions taken. Otherwise you could replace the words "I'm sorry" with any other two words.
Being alone.
What you're saying in your posts are "I'd rather be in a bad relationship than in no relationship". And because you think that way he will cheat again and again. Because he knows he can get away with it with you. The fact that you are so desperate to be in a relationship sets you up to be mistreated. And not just by him. Men that take advantage will spot you from a mile away.
And, frankly, you're lucky it's only cheating. Women that speak the way you do often end up in more physically abusive relationships.
Marriage.
Marriage is Not a magic cure all. The very fact that you think him getting married will magically change him shows how poor your understanding of marriage really is. Change comes from a desire within oneself to be better. If he doesn't have that desire now getting married won't change that. In fact it could make things worse.
Now he'll know your leaving him is much less likely, thus he'll feel he can get away with more.
Marriage is not meant to fix him, or you or your relationship. Marriage is about being selfless. It is about a symbiotic relationship where two people give up themselves for the sake of the other. And that isn’t achieved by just having a ceremony and taking some vows (vows that he's already proven he can't keep).
Cheating men.
Not all men cheat. Anytime someone tells you that all of a certain group does something, know they're wrong.
Forgiveness.
This does not mean you pretend someone's wrong actions, especially repeated wrong actions, are forgotten. It means you don't hold any ill will against them for it.
But you can still use wisdom to see and avoid a problem person.
And it doesn't always happen immediately. Sometimes it's a process that happens over time as you grow and mature.
Can you be sure?
You've found him to be flirty a few times and had sex with another woman. But these are only what you Know about. Can you be positive there aren't more?
What if he changes?
If he moves on to someone else and stops cheating (which is extremely unlikely) so what? Perhaps him knowing he can get away with cheating on you is part of why he was doing it?
And how would you know either way? Or care? You'll be broken up. You should be moving on anyways.
People with the mindset of being a victim always find an excuse to stay with people that victimize them. Exactly as you're doing here.
How about "what if we stay together and he Doesn't stop cheating?". Why are you not asking yourself that instead?
Are You ready?
By reading your posts I'd say the problem here is You are not ready for a relationship. You are desperate to cling on to someone who has already mistreated you. Even to the point of considering marriage.
You have a false notion that marriage fixes people, you don't understand marriage.
You have no belief in yourself, which opens you up to further mistreatment.
You'd rather be in a relationship and cheated on than single, that is an unhealthy mindset.
Forget what he's done, You're not ready. The two of you continuing will inevitably be a nightmare, and you'll be the one to suffer most.
Instead you need to get out on your own, grow, mature, strengthen, learn and enrich your life as a single. Then, one day, if you meet someone that's actually good, you'll be in a place where you can make healthy decisions and have right motives.
Remember, your choices can't be undone. Bad choices can leave a lifetime of regret, and let me tell you from experience, that is a miserable way to live.