Still crushing on my ex...

So me and my ex were together for 4 months but i decided to end it back in march to deal with some personal things i had to fix. It's now 6 months after the breakup and we've. started talking more and i realize i still have feelings for him. The only problem is...my bestfriend just recently told me she has a huge crush on him. It hurts to see them talk and stuff but i know that i shouldn't old her back from going for who she likes. What am i supposed to do in this situation when my bestfriend likes my ex but i still have feelings for him !!??!