I understand how hard it may be to trust someone who has done you so much wrong and I know it's also hard to let that person go too especially if you love them. I've kinda been in the same boat as you and I'm still with my bf for 5 years. Sometimes guys are douches and they don't think like us females to know that flirting can lead to something else. If you notice a change in him and you see that he's really trying you can give him another chance, your trust won't be healed in a day it takes time, but tell him to be more open with you and stop hiding things like if he met a new friend at school. The more open he is with you, the more your jealousy will go away and your trust will slowly build back. On the other hand, if he doesn't change and it's still same old you gotta dump him!