Leaving someone we care about is always extremely hard. Unfortunately, you just need to go through the emotions and embrace the grieving process and allowing yourself to feel all the emotions that come with it. Holding in the crying would only build up and end up eating away at you, so while it is a horrible feeling to feel empty and not enjoy yourself when you are out, allowing the tears to come is healthy and the best thing for you.
Have you thought about trying to find a new hobby or journaling your emotions? I have also found taking long walks and just trying to empty your mind is helpful along with maybe going to counseling to talk things through and get some feedback from a professional.
Although it might not feel like it right now, you will come out the other side and you will be okay. We're all here for you and we know what you're going through.