My background. FWS and I were married for 27 years when I found out he had cheated on me for 23 of them with 14 FB (Fuckbuddies). So he was only faithful four years. We did stay together and were working through it.
So, you wanted to hear from someone who had worked past the betrayal.
Here I am.
Can you work past this? Yes and no.
In the "yes" column he is telling you he is sorry and wants to work past this. You want to work past it.
In the "no" column is he tried to hide it from you until it became impossible because of who all knew. He used the excuse he was "blind drunk" and didn't remember. The OW has been trying to friend you and talk about a "boyfriend" issue she is having (yeah riiight . She's pumping you for info on your boyfriend). You've only been actually dating for a short time and most of that time you two have been apart. It also sounds like he isn't remorseful. He's sorry he got caught; not that he had sex. If so many people hadn't known about him and the OW he probably wouldn't have told you. He has a problem with alcohol.
He's 21 and you are 20. You have no children together, no joined financies, no real history except as long term friends for three years. Is there an engagement ring?
Going through the R process with my FWS was the hardest thing I've ever gone through. Going through his death was a piece of cake compared to working through his cheating. We had decades of history, kids, and money involved. FWS had to hit absolute rock bottom before he was willing to change and do the hard work to fix what was broken in him. Yes....you are only dealing with one infidelity, but he's cheating on you now and you guys aren't even married.
And you want to change him? Like THAT ever works It only works if HE wants to change.
So from someone who worked through the infidelity. Yes it can happen. The cost to you will be never being able to trust him 100%. Living with a person who doesn't respect you enough to honor your relationship together. Living with the "trust but verify" mindset. Living with your self-esteem shattered and less respect for your SO.
It's a tough way to live. There are couples here who have R'ed and who have a strong relationship, but it's cost them dearly and it was a long and hard road they traveled.
You've been given advise here from people who have traveled this road. You've rejected it in favor of trying to work past his cheating. Read with an open mind because we hate it when people are hell bent on repeating our misfortunes when we've "been there, done that, won't make THAT mistake again".
You asked advise from someone who'ed R'ed. I gave it to you.
Think hard on this relationship. He's showing you who he really is.