When you still have feelings for your ex and you have a new boyfriend or girlfriend, it is not okay to be friends with them. I say this because having feelings for them could lead you to cheat on your new significant other. If you do this, then it can have serious repercussions on your new relationship.
In the same way, it is not okay to be friends with your ex when you have a boyfriend or girlfriend and your ex still has feelings for you. This could result in your ex trying to break up your new relationship. Being friends with this kind of ex may give them the false hope that you still might want to be with them. Also, being around them a lot might make them miss you and have even more feelings for you, and that’s not okay if you don’t want to be with them too.
Breakups should be as clean and cordial as possible, and remaining friends with an ex while there are still feelings involved, especially when you have someone new, is not a good idea. Also, I don’t think it’s okay to be friends with an ex if they were abusive toward you. Being around this person may lead you back down a dangerous path.
It is okay to be friends with your ex if there are no romantic feelings involved and you believe that you are better off as friends. I would still suggest taking some time apart from each other after a breakup to sort out your feelings. If after some time you still want to remain friends, then that’s your choice. Sometimes healthy friendships with exes can turn out to be the best friendships of all.