Sex after a break up...
Almost everyone experiences heartbreak at some point in their lives, and most people tend to fall into one of two camps: "The best way to get over one lover is to get under another," versus, "Never again!" Only you know what will work best for you - though if you're feeling emotional, it can be a good idea to keep your friends in the loop so they can help guide you away from damaging behaviour.
In the initial phases of grief, many people turn to drink or drugs to numb the pain. However, if you try to drown your sorrows there's a strong chance they'll float, and it can be easy to make damaging decisions when you're under the influence.
Love yourself, do things that you enjoy and you'll be in a much better state to find a partner.
If you've been with a partner for a long time, it can be easy to forget that protected sex is essential. Even fellatio and cunnilingus have Sexually Transmitted Infections (STIs) risks so you need to stock up on condoms if you want to play the field. Have flavoured condoms along with several different sizes if you have sex with men, and a well-fitted condom that feels comfortable if you're male. Heartbreak only becomes worse if you are having to deal with fears of STIs or pregnancy too.
Just because you're heartbroken, it doesn't mean you should treat other people as disposable. If you're only after a dalliance, be honest with your potential lover before you get intimate. Hurting someone else with lies won't make you feel better long-term - and it can also lead to emotional complications that could easily be avoided.
While you may feel that you'll never meet someone as good as your ex again, that's as much about your body chemistry as anything else. If you love someone, your body releases a bonding chemical called oxytocin, and breaking that bond can be hard. Luckily, time really is a healer: if you avoid contact with your ex and allow yourself time to heal in isolation (with the support of friends and family as required) the (literal) chemistry will fade.
It may not feel like it now, but there will come a time when your feelings will become manageable. Love yourself, do things that you enjoy and you'll be in a much better state to find a partner when you're ready to move on. Or who knows, you might decide you're happier on your own.