It's normal to feel this way. Clearly these people meant a lot to you in some way or another, and when we find to be hurt/betrayed by such people after investing a lot of time and trust it causes us to feel shocked and grieved. I was around the same age as you when finding myself in such situations and it can be tough. It's okay to feel sad but you would need to be specific and think about the situation(s) that caused such conflicts.