Sorry that you are going through this. Yes the feelings can be intense. You may never fully understand them. Sometimes I've found that understanding isn't the goal. Rather the goal is to learn to be ok with your feelings. It's ok to feel scared that her marriage with change things, even if you rationally know it won't.

I hope you can talk to her honestly before the wedding. It sounds like you may have talked about it some already. It may feel good to have her reassurance and insight. It also may be good to have a little bit of a plan for your weekend. Just make sure you allow yourself to feel if you need to feel!

I went through this when my T had his youngest baby. I was the neediest and clingiest client ever. I felt so bad being a little jealous of a baby. I don't think anything helped me, just time to see that things would be the same and a lot of patience from him.