How can you become comfortable being alone when I'm used to being in a relationship
I am sorry to hear of your long term relationship ending. Try to remember that a breakup is still a loss and this is a grieving process, but also try to remember that grief does get better with time. I am completely confident that with time you will readjust to being single (or possibly even find yourself in a different relationship if that is what you want) so that you are able to start finding your rhythm of how to accomplish what needs to get accomplished day to day.
Try to remember that you never stopped being you just because you were in a relationship. Most things you did as a couple you can do independently (though I know it will feel weird at first). Try not to stop doing things you enjoyed just because you are no longer doing them with your ex. Also, leverage this time to connect with other people (not necessarily romantically). When you’re in a relationship long term like you had been, it is very easy to start neglecting other relationships because you are always with your partner. Take the time you now have to reconnect with people you haven’t seen in a very long time or didn't have time to give one on one attention to. Not only will it give you people to talk to if you need it, but you may also even start to find yourself forgetting about your recent breakup and enjoying yourself and able to connect to your sense of self and independence again. Nurturing friendships and non-romantic relationships can show you that you can feel loved and happy outside of a romantic relationship and that romantic relationships are meant to be nice bonuses not what defines your life.
I also encourage you to try something new or to do something that had to take a back burner because it wasn't a common interest of your partner. Ask yourself "what do I want?" Are there things you wanted to do with your ex, but couldn't? New things you've never had time to try? Now is the time to ask these questions, because your answers no longer have to take the other person into consideration. It will feel weird at first but just start engaging in life again. It will begin to normalize.
Most importantly; try to give yourself time to be sad. Again, truly things will normalize again, but it is okay to grieve. You just experienced a loss. Validate that experience and trust with time that healing and refocusing can occur. If that grief and lack of motivation continues though it might be time to consider therapy. A therapist can help you sort through the complicated emotions that a break up can bring up. I wish you the best and that you are able to find your own sense of happiness going forward. Take Care.