Depression at high level. Plz help me!

Hi i m recently going though a break up journey. All of sudden my partner said that we can friend only. And advise me to find any suitable one. I am in this relationship for good 4 years now. Even i tried to think for a differnt partner but again my previous partner's memories keep floating in my eyes and stopping me. I know those days wont come back but to start from the scratch its becoming difficult for me. All weekends i wait for my partner if in question free to meet and mean while i don't respond to other invitations. I know if i meet a new partner after some time i would regret and would hate myself for keeping things hidden from my ex. Now all day night m just recalling those laugh and food..and time spent together.and a lomg wait if by chance my partmer come bsck again. Days  and months passed now m still same. Talking to many but don't have that courage to meet. Feels i would cheat my ex. M feeling very low .no concentration at work. All day just 1 hope.plz help me