Please reply

So my partner is going out with the girls tonight , and I can't come cause apprently she hasn't told one of her friends we are back togather .. but the last time she went out she lied about going out and I didn't hear from her for 16 hours.. and she told me she was home by 11... but she lied.
A friend of mine saw her out, and told me.. and when I confronted her 3 days later and asked did she go out that night she replied with " ohhh umm maybe .. I don't remember .... maybe " then I ignored her for 2 days cause I was crying hysterically being lied to.
Anyways she is going out tonight , and I am feeling so sick about it.. I don't trust her... I am a girl too.
I don't know what to do.. I didn't sleep last night :( I just want to die or run away..