Should i stay strong or jus let go for a while?

Okay so my bf and i jus got hooked up. and we've been talking to each for about 4 months. at times he constantly talks about his ex, he compares us all the time, they broke up two years ago. and yet he complains how she mistreated him and that im better but yet he still talks abt her. how does that make me feel? it makes me feel sad like invisible almost. the more he talks about her the more i can hear in his voice that he misses her and remences about her, even though yet he says he would never ever in his life go back with her, even though also it seems she's found out about me and she's jealous becus she no longer has him. we could be having a conversation in the car and he brings her up, i sigh to myslef, and say in my mind " y dont u jus go back with her? its obvious u miss her?" he talks about her as if seemingly he stll goes with her as if they've never broken up, and yet i am the sideline chick, a moment person, something to conserve time with, not anything special as he says it is.as this continues it makes me think, maybe we should jus be friends for a while more for a sec, jus until he gets his thoughts together. so i wounder should i stay strong or jus let go for a while?