I'm a non EU citizen, and my girlfriend is from Romania living in Spain. She doesn't have Spanish citizenship but has been living there for last 10 years. We want to settle in Spain together but without getting married as we need some more time to finish her studies. So, how can I get a work permit and what are the other requirements for this?
If you are planning on a PhD, then you should enter on that route and be able to support yourself according to Spain's requirements with the respective work limits for that visa. If you are asking as to whether your future intentions to someday qualify for a particular status will help in the present, then no. You will have to qualify on your own right and acquire any status related to your partner at that time when you qualify.