If anyone has any ideas how to fix a broken relationship, I would love to hear it. The first idea on my mind was to try some online couple counseling.

Look, instead on going on a break, you should have sat together and figured out why she had to go behind your back and cheat on you (emotional cheating). Why wasn't she able to openly communicate and work WITH you instead of AGAINST you?

We started dating long distance almost exactly 19 months ago, we both have quite bad mental issues and have been through A LOT together.

Whatever you do, don't fall for the sunk cost fallacy. Have you actually met your gf?

Make sure you talk to your counselor about your relationship too. Make sure you're not codependent with a partner and are able to set healthy boundaries.

She was really upset with me about it at first, considered breaking up because she said it felt like I was stalking her, but calmed down later in the conversation and did forgive me

Did she properly apologise to you? It's a bit ridiculous that she flipped out after SHE was the one emotionally cheating on you.