How do I act towards the guy who broke my heart?

[Oh,HeyYou.]

Hi. Well yeah, I've known this guy for four years and we've liked each other but I never game him a chance bc I wasn't ready to open up for a relationship. That was until a couple of months ago where we started talking a lot more and I opened up to him (finally) and he basically lead me to believe we could have a serious relationship, when the whole time he was lying. The whole time we were talking he had a girlfriend, and I had to find out through a social media website and he didn't even tell me the truth, I had to call him out on it. I spent days crying and feeling stupid for opening up to him, bc that is the hardest thing for me to do! I seriously went through so much emotional stress, I've never experienced before. I was heartbroken basically. I still am, but I've been feeling much better and accepting everything. I have/had so much feelings for him. Now he's all happy with his gf like nothing ever happened between us, but he still wants to talk to me and be friends. The thing is we've been on Christmas break for the past two weeks, so it was easy to ignore him, and "get over him" , well the situation actually, I've been trying to get over HIM. (which I haven't honestly.) But now we go back this Tuesday, and I'm not sure how to act towards him. The last time I saw him before break I had no clue that this would happen. Everything was fine between us. It was the beginning of break where I found everything out. A part of me wants to just ignore him and be a bit*h to him, but another part of me wants to just be friends and use the whole "kill him with kindness" thing, meaning that I won't let him have the upper hand in making me all mad and depressed if that makes sense. I want to be happy, and I want him to know that I am happy, event though he hurt me. This is the first time I've gone through this, and I don't know how to act, honestly. I care for him so much that I just want to be the bigger person in the situation, and honestly, if he's happy, then I'm happy. I don't like to hold grudges, I'm not a negative person, I really am not. I forgive him, but I don't want to seem weak like he can walk all over me. I just know that if we keep talking he'll still flirt with me, bc that's the way he is, and as a result I'll just push him away and be mean. I don't know what to do, please help. We're both 18 and seniors in high school. (Yeah, high school friends don't last as people say or whatever, but still I've known him for four years and don't want to just throw it all away...)

Please help...

[tia]

He lied to you. He is not into you. What he did was wrong. You need to let it go. You need to move on. Ignore him and forget about him. Trying to be his friend so you can kill him with kindness will only stop you from moving on. I understand that you are hurting. But you will hurt more if you dwell on this. The next time you see him, then just pretend that you don't know him. Start dating other guys. Dating other guys will help you to heal.