How do I cope with posttraumatic stress disorder and its triggers?

Have you tried counseling?  Having PTSD from multiple abusive sexual experiences is very overwhelming for one to handle alone.  You may need the guidance, experience and support of a professional to identify all the triggers that effect you and obtain the best coping skills that would work for you.  

Talking about it stops it from being a secret.  It takes courage to have posted your question and that is the first step. Here is an article I wrote a few years back.  http://abuseisnotasecret.com/why-abuse-is-not-your-fault/

One day at a time.  

I'm glad you're willing to keep optimistic about life improving and offering better relationships than some of the ones in which you greatly suffered.

One suggestion is to develop patience with yourself and the process of regaining your willingness to trust other people.

Sexual intimacy engages all of who we truly are.   Being cautious as to who and how much you allow someone into your life, is natural for anyone recovering from trauma.

Allow yourself to withdraw when situations feel dangerous.   Your sense of danger is most likely on higher alert than had you not been victimized.

Be attentive and cooperate with your own sense of readiness to engage in conversation, discussions and sex with your partner.

Explain all this to your partner so the person can develop their own patience with your recuperation process.

I encourage you to seek out and work with a therapist who specializes in treating complex trauma.  Somatic Experiencing, Brainspotting, and Internal Family Systems Therapy are all highly effective treatments for people dealing with complex trauma.  If you are interested in reading a book that is supportive and compassionate, Bessel van der Kolk's The Body Keeps the Score is a wonderful book that discusses treatment options in depth.