Recent breakup

Hey my ex broke up a little over a month we were together for 7 months which was my longest relationship. I dealt with her attempting suicide and going in mental instituitions multiple times. She told me we were gonna get married and that she would never leave me. The other day when drunk I texted her and yesterday I found out the truth. Our whole relationship she was with someone else and she said she's marrying him soon. Hearing that makes me feel like shit. I've been trying not to self harm. I also yesterday got in a arguement with a girl that lives with me that I liked and think she's gone for good. I've been self destructing since breakup using drugs.