Some thoughts on healing from breakups from an attachment model perspective....
It's not your actual ex you miss most after a breakup. You miss the needs that they met in your life. You miss the traits that complimented yours, their sense of humor, spontaneity, assertiveness, etc. So healing and moving on almost requires that you figure out what needs this person was meeting in your life. Once you have identified this, you can start meeting these needs and highlighting these traits by yourself and through your relationships with others. For example, let's say your ex was outgoing and you are shy. Your mind may have attached to this. Biologically, we are all attracted to people who express our repressed or underdeveloped traits. Thousands of years ago, if we were resourceful and we met somebody stronger, we might pair up to have a greater chance of survival. So when we're paired with someone with complementary traits and then lose access to their traits in a breakup, our mind goes through an identity crisis. Back to the example. If I am shy and my ex was outgoing, and we were very social together, now I feel even more anxious about going out without them. So healing is about us being able to realize and promote these traits and fulfill these needs ourselves and through other relationships which we no longer experience through our romantic partnership.
Every breakup has a story, and many of those stories are simply made up (and to our detriment). You want to make sure you're naming and challenging your stories. If we don't do the work to question the stories and reprogram faulty beliefs we've made up about ourselves after a breakup, they can really dig in and keep us stuck in grief. For example, we may believe that it's our fault the relationship ended, or we weren't good enough to be in a relationship with our ex. If we don't work to challenge our stories, then they will become imprinted and realized in new relationships. There's a relationship between "the more stories we tell, the less closure we have" and "the less closure we have, the more our mind seeks certainty by creating stories". Beware of this trap. When our mind is seeking certainty, we'll assign meaning to situations that are both false and often negative and painful.
Time is not what heals, but time is what your mind uses to learn other ways to get its needs met. Time is not the healer but rather time is the medium that allows the steps we're naturally taking towards healing, whether we consciously recognize it or not. After a break up, we typically spend more time with friends and family. This is one way our mind gets used to getting its needs met in different forms. What's really powerful is to recognize that when we begin to try to get our needs met in new ways, it doesn't actually feel good. Why? Because it's so outside of our comfort zone. (Eg. I can't get this need met from my sister because I'm supposed to get that need met from my ex). Yet, through repetition, we reprogram our mind over time, getting used to getting our needs met in these new and different ways (by ourselves and different people), building a sense of self-efficacy, self-esteem and self-trust. This reinforces a belief that we can rely on ourselves and other people around us to meet our emotional needs or whatever needs we felt are missing from that romantic relationship. And this is when we start to really experience enjoyment from getting those needs met in new ways. It no longer feels outside of our comfort zone and actually feels really rewarding.
Staying busy is repression, not healing. The value of time in healing is magnified when it is intentional. Just staying busy or adhering to the old adage, "time heals all wounds", is not the same as healing your mind intentionally. Although your subconscious mind will engage in a process of healing anyway, staying busy does not help the process. You're not nurturing yourself through distraction or avoidance. Staying busy is fine if you're making an effort to do things that are fulfilling, connecting, and strengthening (like self-care), but when it's to the exclusion of actually taking action in your healing process, then that's when it can become problematic. So it is important to stay aware of the ways and the whys of staying busy.
Behavior, not words, grows trust. If an ex reaches out and their behaviors do not show that they are willing to engage with you in new and healthy ways, be warned. Does your ex show up the same or differently when he reaches out? If you both are not willing to put in the effort to do the deep work needed to co-create a healthier relationship, it's a trap, and one that will set you back in your healing process.