1) You said it was a mutual terms break up. She is eventually going to find someone else. Is it somehow worse if she falls for someone you both know and trust to some degree? Would it be better if she fell for some random stranger?

2) Sometimes loving someone means wanting them to find happiness even if you aren't the source of said happiness. If you love her, support her in finding happiness. If you can't do that, then maybe you have been in love with the idea of possessing her rather than living her as her own person.

3) She's going to see you being too friendly and supportive in her day to day life as an attempt to rekindle the relationship. She's trying to establish boundaries to prevent that. As her friend, be someone she can come to if she needs to but stop pushing yourself into her space.

4) Therapy may be useful. Also, find a productive hobby to spend your time in and that you can think about instead of dwelling on the relationship.