I'm no expert and not coming from quite the same place as you, but I came out of a relationship that started in my young teen years and ended in my late 20's. I had a "quarter life crisis" at 25 which eventually contributed to the end of the relationship. Everything about myself made me feel like crap. I felt lost and confused, but here is how I figured it out:
Step 1: Stop trying to be in a relationship. It sounds counter intuitive but really stop trying. Get off dating sites too. You are single, accept this. Really and truly accept this. Don't hide it, don't be embarrassed by it. Yes...own it. Keep reading.
Step 2: Start going out to more social events and have a good time. Join a social meetup.com group for Photography, hiking or even just a happy hour group. Be yourself, be relaxed, talk to everyone, don't try hard to be funny, just try to have fun with the people around you. Try new things that you never had an interest in before.
When meeting new people try to avoid the "What do you do / Where are you from" conversation. Not saying this line of conversation is all bad, but actively seek out something a bit more interesting to start out with. Talk about the news, the weather, the new iPhone, your love of dogs, your weekend. Keep switching topic themes until you hit on something that the other person really gets into. Think of conversation like a metal detector...you keep swooping around and you get faint pings back. As you get closer to real treasure your focus in on that area.
Step 3: Learn to flirt appropriately. This takes practice and you'll probably mess it up...You're probably already messing it up, don't worry you'll always mess it up sometimes. If you find a manual online for how to do it, just ignore it. Everyone is different: different personalities, different pasts, different sense of humor. Once again just like the metal detector metaphor, just keep swooping until you find whatever works. In general you want to make it clear that "I'm into you".
Don't always feel the need to rush to this right though. Sometimes you can start flirting right off the bat, sometimes you'll know someone for a while before the moment is right. Use your best intuition.
Step 4: Eventually you and someone else will hit it off. Ask them out. Just do it. Worst they can say is no. If they do say no: take it in, yes it might hurt a little, scar the ego. Think of it like applying to a job. Sometimes you just get a no. Move on. You want a response along the lines of "Fuck yeah! Let's do it" instead of trying to convince someone to do something with you.
Also if you think you've hit it off with someone, don't push too hard and come off as desperate. Don't take it personally if they just fade away. There are so many reasons why they may not want to go out with you: They may be still getting over a previous relationship, they may have some family issues which takes priority, they could just have gotten busy at work, might be moving soon, you might remind them of their dad, you might remind them of someone with whom they have a negative memory of or a whole other range of reasons. All of which have nothing to do with you.
Step 5: Keep taking care of yourself. Dress in a smart and modern way. Note: I don't mean go buy a new wardrobe, but do take a hard look to see that you're not dressing like a complete slob. Ask a close friend for feedback or check out /r/malefashionadvice.
Hope this helps.