I can't tell if the thoughts and dreams I'm having about my ex are me missing her or the thought of her. I appreciate your advice and help!?

I am 23 with a girlfriend of 10 months. My ex and I dated for 18 months, but broke up late 2017 and haven t spoken, text, or talked to each other in about a year and half. However, over the last 5 months I've had 7-8 dreams of her (either dating or being married to her) and certain words people say will trigger memories of her. For about a week now I haven't been able to get her off my mind. I feel bad for thinking of my ex while dating a new girl, but I can't figure out if these are feelings for my ex or missing the thought of her. While dating my ex we had talks of marriage and engagement. I've talked to some people who say the dreams and thoughts could be me missing my ex, or it could be me simply needing to figure out what my current girlfriend is to me concerning marriage. Do you have these thoughts and what is your opinion?