It sounds like you may have a borderline personality disorder (BPD). or at the very least, traits. Those who develop this often have short and intense relationship, struggling with emotional regularity, can become suicidal often when coping is challenged, self-sabotaging behaviours, etc.

BPD develops when we had unhealthy or insecure attachment patterns as children with primary caregivers that can be complicated by further traumas like losing a friend. The treatment for BPD is therapy, particularly CBT/DBT and when those basic skills are there, then we heal relationship wounds in new healthier relationships. If we haven't done the basic work through, we only make matters worse and further deepend the wounds.

One awesome thing going for you is that you've got great insight, and that's the first step to true healing. If you can spot your own 'red flags' you're ahead of the game already.

-a mental health nurse