The feeling of missing him is quite neutral. You are still getting used to the fact that you are no longer a couple. Him posting pictures of the two of you is also sending some mixed messages.
You have to remember what caused the break up. Focus on that decision you've made and the causes for it (something had told you that things were not working out) You do not want to sabotage yourself.
When you start to think about him, try to direct your attention onto something totally different. The thoughts are something you have control over. Try to think about the reasons for splitting and then observe your thoughts and let go. Just try to stay mindful of when you think about him (you said when you are at home. If you are bored, lonely, tired, then do something to take your mind into another direction) Reprograming your thoughts is possible.
It's Called a Breakup Because It's Broken: The Smart Girl's Break-Up Buddy by Greg Behrendt and Amiira Ruotola-Behrendt (Paperback - Sept. 5, 2006)
That may be something he is doing on purpose (to see your reaction/revenge/remind you of himself, etc) The speculations can be many. Only he would have the answer. Ask him (or if you are not comfortable, let him know you would not want your pic posted)
If you are alone before you go to sleep, you have that window of time open to think about stuff (thinks you need closure on)