Most Helpful Guy
A famous psychologist once stated that people find partners the same way they buy cars. They look for the best deal they can get with what they have to offer. Your story reminded me of a car I once owned and loved, but no matter how much money I put into it something new always broke down.
Haha. Well, people aren't cars of course. But you are young and have lots of miles ahead and, I am sure, deserve more than what this guy has to offer. It seems you might not want spend time and effort in shopping around for a better partner. It could be that he has trashed your sense of self-worth and you think this philandering dude is what you deserve.
The first rule of thumb is that an ideal partner must contribute to your well-being and self-esteem. Why get into a relationship that works against your own best interests? The trust you had before will never return after he has betrayed you. Do not give him a second chance.
Get rid of this creepy guy, update your wardrobe, and start actively meeting appealing guys more worthy of you. You will have to do this cold turkey because you have become addicted to the notion of love itself, not this guy. You may feel down a few days (just like anyone who loses someone they were fond of) as you did when he left, but you will get over it in a few days. Meanwhile, stay active and catch up on your reading, take self-improvement classes, and find out where to meet nice guys and go there, with a girlfriend maybe. Nature will work for you.