@saddie,
You might want to get a new therapist (note: I am not a doctor).
Why? Because that is some horrible advice right there.
Here's my suggestion to you, particularly because I have no idea how long it's been since the breakup with your big-time ex:
Don't date. Don't try to be with someone else for the time being. Instead, work on yourself. Do something which is self-improving, whether that's to go to a gym or take a class or read books or travel or volunteer or make art. Do something completely and utterly for you that, when it's finished, makes you a better person in some fashion.
How long should this go on for? I don't know. I am thinking maybe a full semester's worth, even if you don't end up taking any classes. So, about three months or until you are finished with whatever it is you are doing to improve yourself, whichever comes later. And then evaluate. If you want to keep going on self-improvement, then do so. If not, then consider yourself finished and that is fine.
Why am I suggesting this? Because I think your self-esteem tanked. And I truly think it tanked when you first met this guy and not during or afterwards. Why? Because he treated you poorly and you fell for it hook, line, and sinker.
So you need to shore up that self-esteem. Become awesome at pottery or knitting or cosplay. Get an A on your European History paper or bench press 240 or whatever it is that spells awesomesauce to you. And then when you see this guy again (and you will at some point), you'll be more confident and he won't matter as much.
And you'll also be reminded that you are a fine and lovable person, and you deserve to have someone treat you well.
Don't write off love. Don't write off people. It can happen again. But you need to pull yourself up first.
Now go out and slay some dragons.