How do i know if I am making the right choice for myself or if I'm just hurting myself emotionally?

It sounds like you are struggling because you like this person and she likes you too, but you want to be monogamous and she does not. You can start by identifying the pros and cons to look at the situation objectively to help determine if it is worth remaining in this situation. For example, a pro may be that you have someone to spend time with, or you have certain things in common. A con may be you want a deeper commitment, or you want to feel at ease when you are dating someone. If you want to feel at ease in a relationship do you think you can do so with someone who wants to be intimate with another?

Another way to explore this situation is to identify what your values are and investigate if your actions are aligned with your values. Research indicates that when our values are not aligned with our actions, conflict occurs within ourselves. Ask yourself is it important to be in an intimate, caring,  monogamous relationship with someone who wants the same thing as I do, or do I settle for something less than what I want? 

It was written that: "I am being stupid since it is bad for me mentally". Often times self-criticism arises because of how we were conditioned in the past; perhaps, an adult spoke to us in a certain way as a child and we internalize this type of language and therefore speak to ourselves like this. It could be that inner criticism arises with the intention to help motivate us to change. Even though there is good intentions, we end up attacking ourselves which activates our threat-defense system.  Activating our threat-defense system causes cortisol to be released which causes stress. Try to turn towards yourself in a loving way. There is no shame in wanting to be loved and being naturally attracted to someone, but try to explore and determine if this is what you really want. How do you think you can create the life you want? What is the first step?  

I wish you the best on your journey,

Eri