What my best course of action here. my two good mates are about to start a relationship, and ill be in the mid?

Don't cut ties. Just be friends with both. You just have to watch what you say very closely. For example when one of them is talking bad about the other, just ignore it. Don't talk about what the other says about the other. Don't be an instigator. When one wants to talk, just listen and get advice. Just be yourself. You've been in this situation enough times to know that you can't tell everything.