Here's the thing about love.
It's not enough.
If you want to, google "love is not enough" and see what comes up. I found lots of very interesting and illuminating things!!!!
You may get to the point where you love him enough to stay, and that will likely depend on how he rises to the occasion of actively repenting and mending the deep wounds of his betrayals by growing as a man and a human being.
And your love for him, well it may or may not be enough, for you to stay. Marriage is way, way more that just about love. Most of us really don't understand this until we've hit several trials and tribulations.
It's also not enough to stay for the kids. Marriages that exist for the kids inevitably do not work; they exist, for years, but they are generally not good.
You are both very young. His ONS with your XBF (soooo sorry!) happened when plastered. Okay MAYBE he's just immature; a 28/29 year old man's brain just maybe was formed finally at 25, and some say it takes until they are 43! In any case, you're both young and not to give him a pass, but plastered new year's eve parties for immature people without boundaries are trouble waiting to happen.
The good thing is that you don't have to decide now. You can go to IC, MC and see how it goes. If you really go down this path, without rug sweeping (!!!!!), you will learn a lot about yourself, him, marriage and life. It's a path of growth and I hope for the sake of your family that you can work it out, but if you can't for whatever, you will learn that too and come to peace about it.
I'm glad that you are not scared of leaving him. It's good to read that!
Best to you!