Please help me

I feel sick when I think about my ex and his new girlfriend. I really want to be happy for him and not let the past drag me down any longer, but this is my first breakup and seeing him move on is harder than I expected. I thought I was over the breakup but now that he's in a new relationship, all the old feelings of poor self-esteem, anger, confusion, and now, jealousy, are coming back. I keep comparing myself to her and I feel so inadequate. I know it's dumb, but I feel so alone and it seems like I'm the only one going through this awful pain. Please tell me that it will get better because it's really hard for me to imagine this heartbreak ever going away!