I started going out with this guy in October and then he dumped me because he knew that

I liked this other guy and now me and him are going out!
The guy that I am going out with now... I don't really like him as much as I thought I did!

I like my ex!

Can anyone help please?

I need advice on what to do!

Do I stay with the guy I'm with now or go back with the other guy?

Sometimes it is best to break up and take a step back and focus on you and wait for the right time to work things out with getting back with your ex. Jumping in and out of relationships could make the ex feel like you are unsure, insecure and so forth with who you are and what you want.
Also you need to take into consideration if he might not even want you back. Many people make a rule for themselves that once someone breaks up with them they will not take them back.
What he wants and feels is a lot to be taken into consideration.

I agree with N0help4u. Even if you're having a good time with your current boyfriend, I think its best for you to cut things off for a while, just to get your thoughts in order. Spend some time doing things you like to do with your friends. Make sure both your current and your ex understand that you just need time off if you decide to go through with my advice.