I cannot tell you the number of rebound relationships that I have heard. Maybe you have gotten into a few yourself. Why do they get into another relationship a few weeks or days after we just got out of one? Maybe they did it because they wanted to mask the hurt and pain of the break up. Heck, they just wanted to make the pain go away and getting into another relationship seem to help or at least bandage the wound.
I soon discovered that rebound relationships rarely work out, they are...well, rather temporary. Nine times out of ten they just don't last very long because they get into a relationship with the wrong person for the wrong reasons. Getting into a rebound relationship only causes more trouble and leads to yet another break up. A vicious cycle indeed.
So rather then finding yourself in a rebound relationship shortly after a break up - try this; first relax, and breath for a moment. Whatever feelings that you are going through, go through it. If you feel like crying, go ahead and cry, and yes "real men do cry." If you feel like having a couple of drinks, go ahead and have a couple, write an angry letter to your ex, but don't mail it. Eat that bag of chips, punch the pillow, cut up pictures of your ex, talk to a trusted friend. Safely...let yourself feel or experience whatever it is you are feeling in the moment. Why? Because it's perfectly normal to feel hurt, depressed, confused or angry after a break up. Releasing your pain in a healthy and harmless way can be very therapeutic.
Rebound relationships are not healthy for you and it does the individual you are in the relationship with a grave injustice. It's not right to use someone so you can feel better about losing an ex or use someone in an effort to get over your ex or to get your ex back. It's just not fair and it leads to more pain. Instead give yourself time to get over your ex and move on from there.
If you truly were a good partner and your ex left you and quickly got into another relationship (rebound relationship), it is only a matter of time before your ex comes to his senses. If you are waiting for your ex to break off the relationship and come running back to you, you must exercise patience. This may not be the easiest thing to do because there is no specific timeframe as to when a rebound relationship will go sour. And yes there is a slim possibility that things could go well. Rebound relationships rarely work out...I did not say they never worked out.
So the bigger question is - how will you find out how your ex and the new partner is doing? You will need to know if things are going well or if they are rocky. Well, if you live in the same town as your ex and frequent the same places, have the same friends - you will start to hear things about your ex and their new fling. You may still be close to some of your ex's family members, you can find out from them how things are going. So basically anyone that you both use to hang out and associate with is a potential source of information. Keep your ears and eyes open for signs that things are not going well.
The sooner things start to go bad in the relationship, the better. Better for you that is. It is much easier to break off a rebound relationship when you have only invested a few weeks into it. When he/she comes back to you - the ball is in your court- it's your call as to how you want to handle the matter.