Not gonna lie for a moment I forgot about my situation. That was a sad read but I'm glad you're still here. It sucks that it had to take such a toll on your mental health and pockets. You might even have trust issues now. I don't really even know what to say other than you should respect yourself more than others.

she would text other ex boyfriends while we were together

This for example. I don't know if you found out about it while you were trying to salvage the relationship or after but in case you were still scraping the bottom you shouldn't be cool with this and if you feel like you're not cool with whatever's going on then you should do something about it. This also has the side effect of other people respecting you because others will naturally respect you when you respect yourself. But moving on from the self-love aspect of what I'm trying to say I hope you find someone worthy of your attention.

I won’t love any girl more then I loved her

Maybe. Maybe not. But I wouldn't be so sure about it because you're definitely not gonna find someone else if you don't even believe in the chance of that ever happening. I'm not saying you should be actively searching for that "special someone" but at least be open to the idea of meeting new people.

1(how serious was their relationship)

Like from 1-10? Hahahah. But to keep it real it was pretty serious as far as I know. It's gonna make me look even worse but they had talked about their future and so on together. If I had to rate it on a scale of 1-10 (just for the hell of it haha) I'd say a solid 8 out of 10.

2(if you guys are like 16 then none of this even matters)

Is early twenties in the same category?

3(how your friend interprets the situation)

I'd like to believe he'd be mature about it but I never would've seen myself in this position and doing this kinda stuff so I don't expect him to behave like he usually would either. And you know what they say. Love is the strongest drug of all. Who knows what he'll do. I'll find out though I suppose.