Why would it matter unless you want the ex boyfriend to be Jealous?. This is how you know if he`s jealous, He probadly wont talk to you anymore and if he does he`ll ask you questions about your new boyfriend like for example "Is he better in bed than me?." Or anything about your new boyfriend, See my ex is the same way I'm in the same boat I dated my ex for 8 yrs and now I'm with a different guy (much better guy in fact) anyways, I know he is jealous because he now has a girlfriend and he brings her with him to pick up our son like he`s trying to say "haha I got one too." And he`ll stare at me, Or he`ll look away from me, If my boyfriend is with me he wont even talk to me, He even gets jealous if he is standing behind me he`ll look at my boyfriend with an evil look then look at me (up and down) then turn and walk away without even looking back, So to answer your question its possible that he`s jealous and then again he probadly doesnt care and is moving on with his life. Good Luck hope this helps. Another way to tell if they are jealous is if they tell you or they call you one day out of the blue just to have a talk and you end up talking about your relationship together or how you both was in bed, Men can be really confusing, Wish there was a book out there about this stuff.
When you see your ex, and he is constantly talking about your new boyfriend, then the guy is jealous.
Why would it matter unless you are either vindictive or jealous of your old boyfriend and using the new boyfriend for revenge.
When he is standing in your front garden with a chainsaw asking if you guys want to come to a barbecue!!!