It's been a hard week

I went through a breakup with my boyfriend of 6 years two months ago and he's now dating someone new. I thought I was moving on for a bit and I was even feeling happy for a little bit. But this week has been so hard on me. I don't know if it's because it's been raining and gloomy all week where I live, but I've been feeling really sad this week. I don't know how to get past this and I honestly feel like I'm going backwards. I hope that when the sun returns maybe I'll be happy again. But I don't know. I'm just really tired of this long period of sadness. I want to know when I'll be happy again.