it depends on you. do you see yourself marrying him? i think it’s a little unreasonable to not expect ur partner to ever have small crushes on other ppl, but it is the flirting/pursuing it in this situation that makes it difficult to overcome. you will likely need lots of reassurance going forward if you choose to stay and he should respect that. take it day by day and see how you feel. there is no right or wrong in this situation, only what’s best for your future self