This is my personal opinion, so take it as you will.
I think it is perfectly acceptable to still like your crush. The two of you did date, so that shows that you liked each other enough to move onto the next step. Even though you two broke up and are still friends, you can still have feelings for that person because of all the time you guys spent together. And I cannot guarantee that you will get over him, because you may not, you might though.
Also, because you have feelings for him doesn't mean the only relationship you can have is that of dating. And I am not sure how long you two dated, but it has only been four months, and in retrospect that isn't really long at all. Maybe that fire will die down when you find someone else that you are interested in, again it is a possibility.
All in all don't just focus on the fact that you have strong feelings for that person. If you do have them, being there with them, having fun, should be enough for you. Don't try to go too fast. Remember, slow and steady wins the race.