Stay strong, I know it is hard. But do whatever you can to not think of her and just focus on him and you.
How long ago did you break up? Got to ask why he told you this stuff, to make you jealous perhaps?
Look at it that things are now simpler for you, now you can spend more time focusing on your Self Love, which by the sound of it you really need. If he's rushed into this relationship it's likely it is a rebound and that it will only show him how much he misses you.
At the end of the day he is still speaking and contacting you so still has feelings for you.
Just step back and work on yourself right now, don't message him. He will wonder where you have gone and if you have moved on. Then when he does come back you will be in a state of not needing him because all the love you need is within yourself and that will be so attractive to him!
The answer to your question is YES, OF COURSE you can attract them back. Try the 25 day challenge if you like, but if your feelings are still raw right now then put that on pause and do self love until you can let go and focus on him with only positive thoughts about your future.
I took a break from the 25 day challenge to do Self Love and am so grateful that I did so. I'm not saying not to do the 25 day challenge, but may sure that right now at least 75% of all your effort is on YOU and LOVING YOURSELF!
You can be anything you want, never forget. It might seem like a set back right now but once you love yourself more you'll be thankful for it, trust me.
Much Love