I feel inferior to people in relationships

Whenever I see a happy couple, my mood immediately goes to shit. I could be having the best day of my life, everythings going great, but once I see two people holding hands, kissing, or doing ordinary couples stuff - it's like nothing really matters anymore. At that moment, I don't feel joy anymore, my mind becomes fixated on the idea that I will really end up alone, and that being better off dead is probably best. It's not healthy, but this is the reality I live in. I click with people, but when it comes down to being more than friends they're always not interested, in a relationship already or whatever bullshit reason they can come up with so they can distance themselves from me. It just makes me feel even more fucking worthless as a human being that I can't achieve anything so simple as being in a relationship. I'm a fucking loser and a creep. It doesn't help that everyone around me finds love so easily, like literally within the span of a week of meeting, they're already committed to one another. Why can't that be me? It's as if I'm destined to end up alone, god himself drawing up the perfect plan to not have me find love EVER. Thank you for reading my incoherent thoughts.