Welcome to the forum and well done for sharing your current situation with us, its a very brave and positive thing to do :) I'm so glad you have such a loving partner in your life and that you get along with him so well.
When I read your post I felt I could relate to you in a lot of ways. I am quite similar in the sense that I have been with my girlfriend for about 3-4 months now and I love her dearly and feel we are a fantastic fit together, but I also have been developing the anxiety of late, especially when separated from my partner as well as anxiety at work.
I'll start with the 'separation anxiety'. When you aren't around him, do you feel anxious because you feel like something bad will happen to him, or is it more that you feel more safe and secure when he is near? Or possibly it could be both! For me personally, it is both. Some things to think about or consider may be, is there something in your past that is leading you to be worried when away from your partner? Perhaps the sudden loss of a loved one in the past that has you worried that you may suddenly lose your current partner?
Now regarding your job, its so great that you love your job, because that is very important! Especially when work is a huge part of our lives. Panic attacks at work can be the worst especially when you can't go home or get some quiet time because you are so busy. I find that even if you can go to the bathroom for 5 minutes and do some deep breathing and try to calm your mind is helpful for me, it may be worth a try for you if you start to feel like the anxiety is building?
And by the sounds of it your partner is a very loving and supportive person and I'm sure he would understand if you explained about the hard time you are going through at the moment. I find sometimes putting your thoughts down on paper in the form of a letter is a great way of communicating these things that may be hard to say in person. And you can take the time to write down exactly what you want to convey to him, and it also gives him the chance to take it all in a take the time to reply to you, without the 'heat of the moment' getting in the way so to speak.
Just remember, you are not alone. So many of us feel very similar to you, and there are so many ways to work on these feelings so you can ultimately feel better. You have taken the first step and reached out, so well done. Hopefully I have helped and if you have any questions please let me know :)