Lady, you don't need a boyfriend, you can just have fun all by yourself and do your own thing and go where you want to go. Besides, you'll have more freedom on your own anyway, and you'll have more control over what you want to do, how much you want to spend, when to do what, and so on. When you're with somebody, it's always going to be compromising this and/or compromising that and making sacrifices for each other.
You can try and contact an ex, but they might just ignore you if they're already moved on by now even if they haven't themselves any new girlfriends or anything. Or they could have realized that they feel more relieved that they have much more freedom and control compared to when they had been in any relationship and now decide to go their own way and do their own thing, their own way, on their own time. Whenever, however, wherever they feel like.
As a boyfriend? Probably a bad idea, it ended for a reason and you don't HAVE to be in a relationship, if there's nobody to have then it's fine to have nobody. As a fuck buddy? Go ahead, just make sure it's understood that you're just fucking
definitely NOT! Been there. Done that. You'll wind up in an on again, off again relationship. Or, with a friend with benefits that gets weird when you find someone new. With me, they get possessive. You might even wind up with a stalker.