As much as I'd love to be able to say there's an easy way to move on and let go there really isn't. It's a process that is individual to each of us and depends on the details of the situation we're dealing with. Time is definitely a healer, as is being kind and patient with yourself as you transition through any difficulties and challenges in your life. Here are some other tips to help you along the way:
Too often we look to other people to fulfil a need we have and we look to other people to create change instead of creating change ourselves. Every challenge we face is an opportunity to learn and grow. In fact that's exactly why we have challenge. So if you're dealing with any difficulty in your life or with others instead of looking to them and focusing on what they need to change, look within at what YOU need to change.
We are the creators of our lives and as such we create everything that happens to us, either through our beliefs, our thoughts, our emotions, our actions, etc. Taking responsibility means accepting your part in whatever situation or challenge you find yourself in. When you take responsibility in this way it empowers you to be able to create change. If you get stuck in victim mode and continually place blame on others for the things that happen to you in your life you'll continue to stay stuck and find it difficult to move on.
Focus on what you want
It's very common when faced with a problem or an issue to focus on the problem rather than the solution. However by continuing to focus on what is wrong or not working well we continue to create the same experiences in our lives. You must be willing to let go of the past and focus on what you want. When you keep your focus on your desires you are manifesting that outcome into your reality.
Look beyond one person
When it comes to relationships, of all kinds, we can sometimes put too much pressure on people to be everything to us but we have multiple relationships with people because each one is an opportunity share something special and unique. We tend to do this more so in intimate relationships so If your partner is not very good at having a deep and meaningful conversation for example, but is great in most other ways then you'd look elsewhere to have that aspect fulfilled, most likely with a friend.
The most important relationship you will ever have is the one with yourself. As you focus upon fulfilling your own needs, your learning, your growth and your personal development you build your sense of self-worth and self-esteem. The healthier your relationship is with yourself, the healthier your relationship will be with others. So shift your focus inwards, focus on what it is you do want, take responsibility for yourself and your life and let go of the need to have one person be your everything. Do this and you'll be well on your way to happiness!