I feel with you! I am in a similar situation, for different reasons.

I just figured that these strong feelings are almost like a panic attack, so right now I am trying to treat them that way, with some tiny differences.

The first thing I would do is to delete her facebook sign in from your phone, and to actually unfollow her actions on social networks. You are close enough to her on a daily level. Otherwise you get worked up in a network of triggers and the desire to control each and everything, which you can’t. It gives you and her more freedom and is one step to learn letting go.
You cannot prevent anything from happening, or her from leaving or being tempted. She has decided for you, because you are a wonderful person! And even if she decides against you (I’m triggering you right now ;-)) you still stay a wonderful person!

The other, more important thing you could do (which I just have been doing yesterday and still feel excited about because it was such an insight) is to write down EVERY possible trigger:
Which behaviours? Which situations? Which thoughts?

Then write down which fears are triggered by that (be as precise as possible), and which beliefs work behind these fears. (For instance “She will leave me for someone else.” (I’m not good enough)
“I will go crazy.” (I cannot survive on my own)
and whatever you can think of.

There are usually different parts in you that try to protect you. With me I have a part that blames and gets angry and wants to end the relationship to prevent getting hurt. Another part I have is that of a child that was helpless and left alone, and now is afraid of not surviving and gets very sad and afraid and desperate.

In the end you need to find out what these parts are in you, and understand and accept each and every one of them. When a trigger comes, you can listen, see what the trigger is, follow the thoughts and fears that come up and identify to which part they belong. It’s pure analysis, but it helps, because it teaches you to seperate the situation from your feelings and to accept these feelings and the parts of you that create them.

One more thing that might help is A) a letter you write when you feel good about yourself. It should be a compassionate letter from your grown up, healthy self to your hurt and vulnerable self. Tell him that it is ok to feel this way, that you understand him and that you will be with him! Read it whenever you need to!
I don’t know if this is a good idea or if it leads to too much dependancy, but you could also ask your partner to record a message for you, that will tell you that she is with you and loves you and that it is ok how you feel.

I hope this will help. Go on looking for help and don’t give up! You can do this! 🙂