What should I do...?

So it's a long story. I met up with an old friend from middle school in a game a few weeks ago, and so we added each other as friends and then we would sometimes play together in multiplayer.

So one day, he told me about his love life and crush since his high school days, their relationship was a bit complicated tho (both of them were at flirting stage but it was one-sided) However, the girl was often cold towards him and barely even talk to him. Shit happened, and they were in the verge of breaking up.

So he was a bit depressed, and asked me if he should continue this relationship or give up. So i told him to give up and maybe try to take good care of himself first.

And then out of nowhere, he asked if i can help him give up his relationship, smtg like starting over with me. And out of impulse, i agreed, but it will only be a trial period, we try to spend some time with each other to understand better. And if we like each other, great, if we don't, we can still remain as friends. And he was ok with it.

So it has been abt 2 weeks since the trial period. The atmosphere was good and sweet, we were drunk on our hormones and serotonin, and he is definitely happier than in his previous relationship. And now he wanted to make our relationship official. I was also okay with it. It was a big mistake.

Because out of nowhere, i suddenly feel skeptical, and i panicked. The feeling is like "what the hell did i just get myself into???" Ok sure, the guy is decent enough, his looks r average, he's also a capable guy. But the thought of my personal space being invaded scares me. I also felt like i cannot fantasize abt my 2D husbands anymore...(cuz it feels like I'm not loyal). So im in a dilemma ...i wanna tell him that our relationship is not going to work out but at the same time i dont wanna hurt this guy....what should i do ...?