[UPDATE] I (20F) started liking a new person (19M) as soon as I started dating my talking stage/situationship (20F). what step do I take next?

As mentioned, I (20F) had been talking to this girl (20F) for 10 months (sort of a situationship idk) and we had decided to talk exclusively to each other. Recently, before I made it official with this girl, this guys (19M) asks me out but I turn him down and offer to be friends with him instead. I have been talking to the guy for 2 weeks now, but I feel like I'm starting to develop feelings for him. To shut how I feel down, I asked my situationship out to be my girlfriend and she said yes. But my feelings for the guy has just intensified. Today morning I got upset that he hadn't texted me back during his usual time last night.

Some more context, my now girlfriend and I are doing long distance and we have barely met each other (twice). The guy is someone on campus. The guy and I have spoken twice irl and the second time was yesterday which I feel like i flubbed and I still want his attention after that and I'm beating myself over it. My girlfriend is absolutely wonderful and genuinely a great person, and has been a great partner to me even when she didn't have to. That's why I feel even worse for emotionally drifting off from her. I want to break it off with her but I don't know what reasoning to give. My initial plan was to end things in summer but I don't want to wait till that long. I want something with the guy. What do?

**[UPDATE]**

I broke it off with the girl and I came clean to her. I apologised to her about breaking her heart and I do not wanna do anything like this to anyone ever again. I talked to the guy as well and admitted what I had done as well as the fact that I did like him. He said that he also still likes me and wants to pursue me. But I need to sit with myself to figure out my own moral standing and direction as to where I wanna go. Another added layer is that I have told people that I have a gf and now I have to break it to them that I fucked up this way. And I know I will lose people because of this definitely.

I am at a crossroads of where I stand morally and I wanna do right by both the guy and my ex. I don't want to pursue something with the guy because I feel like I will be betraying my ex gf. But a part of me still desires to pursue something with him. Do I pursue something with the guy? Or end things with him as well to respect both of them?