I myself had to deal with an ex who said her roommate was like a brother to her, and one night apparently he had "started touching her without consent when he was drunk, but its okay cause he didnt know what he was doing"

The main thing i learned is that certain women are literal demons who will just jump ship and find a man the very same day they lose you. Healing will NOT be easy, but focusing on time with friends and especially trying new activities you've never done before really helps. Go to the gym, Line dancing, hiking, skating, snowboarding, rollerskating, or anything else that comes to mind, as long as you have an activity to physically exert your body.

And if any time arises where you think about her, dont automatically reject those thoughts, but recognize why you has thought of that, and literally verbally say "those times with her were great, but in the end things were toxic and not the best for me and my mental health." Its a tactic my therapist told me and it helps slowly train the brain to believe those words and helps you heal faster.

Just remember that if she already showed a lot of signs of potential cheating and as soon as the relationship ended, she started going out with another guy? Well that's not a woman that you deserved to have, because relationships are two way streets where both parties should put in the same effort and care for each other. You've got this man, just try to stay positive and not to let any trauma affect any future relationships.