My long term girlfriend talks with other guys like she's single, what should I do?

Relationship issue. Talk to her. Learning to talk with each other about feelings and relationship issues is essential. But you must be willing to listen in order for this to work. A resource for couples learning to communicate is www.Gottman.Com if you are serious about your relationship consider a couple's communication class or a therapist that can work with both of you.
Talk. Talk to her about your feelings, and focus on yourself or she may get defensive. Maybe you feel threatened, under-valued, or jealous when guys think she is single. Maybe she is not trying on purpose to "talk like she's single." ask her about her perspective. You gotta be honest and communicate for a relationship to last.