Serious relationship question!! 18 or older answer please?

Sorry its so long but i had to give ALL the details in order to get a legidimate answer. Thanks in advance!!

Okay, me and my man have been together for 4 years and have had a very good relationship up until this past weekend. We usually dont go to parties but one of our friends were having a graduation party and we were invited to go. So of course we went and at first it was alot of fun at the first party and everything was going good except for the fact that my man was already getting extremely drunk and beligerant.

Once that party was done we were also invited to the "afterparty" in another town. We get to this afterparty and there was SOO many people i havent seen in a long time so i was having fun at first. Then my man started talking to this girl whom i dont know but ive heard from my bf and his friends that my man smacked her *** at a party a long time ago when she had a bf. So that alone wasent enough to get me upset or mad but what he said to her did..he said "whats good girl i havent seen u in a minute why u look so mad last time i seen u, u were all smiles!" In an extremely flirty way!

i was like excuse me?!? and pulled him aside from her and started yelling at him for flirting with some ***** right in front of me!! It was the fact that he ignored that i exsited that got me mad not just talking to this girl. Its one thing to say "hey whats going on havent seen u in a while, (shake her hand) have u met my girlfriend?" That would have been the respectable thing to do. But sence he was so obliterated he didnt even comprehend what i was saying to him (by the way i dont drink at all).

So after that happened i was so furious but i let it go and stayed at the party. Then he was getting a keg cup and some girl came up to him and said "u work at mikes shop right? and hes like yea and she goes yea i see you ALL THE TIME! and he goes yea i work on ur car everytime its in the shop" i asked her who she is and i still have no idea who this chick is...she was flirting with him again right in front of me like i didnt exist.(by the way when i confronted him the next day he claims he dont kno who she was)

So i told him i was leaving because i was sick of this party and he refused to listen to me. So me and my girl walked out to my car to wait and see how long it took for him to realize i was gone and it took him literally like 10 minutes to finally come out front. To my 3rd surprise for the night he walks out with TWO GIRLS!!!! and he was like "wheeeeeww LS vtec *****" (if u dont kno what that means its a motor to a car)

By this time im so beyond pissed i did a burnout in front of this house and sped off. That night he called my phone like 5 times. The next morning he called me like 20 times and i didnt answer any of them because i wanted him to get it threw his head i am not putting up with this ****..so finally he tracked me down on my way to get gas and we argued in the gas station in front of everyone..lol i really didnt care who was around.

He apologized and i know he was sincere because of the look in his eyes. I laid down the law and explained if anything like that ever happens again were done for good and i was dead serious. He vowed to not go to anymore parties and that hes not drinking again for a LONG LONG time. Im not sure if he deserves my trust again or if i should just give him this one chance to prove himself or its over. I love him to death, hes my best friend and my man for 4 years and hes never done something like this before to me. (only reason why hes getting another chance)

Should i have a reason to still be resentful for what he did or should i just let it go? I kno i gave him another chance and i should give him the benifit of the doubt that he will redeem himself but i just dont know. What do you think??

BTW: im 20 and hes 23 if that helps