Your intuition to do some counseling is a good one. The find help tab at the top of the page will help you find someone in your country.
The more intimate relationships have different rules of engagement because of the intensity involved. When you are single and dating is casual you don’t have much to lose because the investment isn’t so great. But it sounds like once you are emotionally invested it feels shaky because now have something to lose.
Just because you have a feeling of being insecure doesn’t make it real. When you feel these concerns, particularly about your jealousy, you are going to want to challenge these thoughts. I would encourage you to work with a therapist who can teach you the basics of resilience so you can have the thoughts and move past them.
The find help tab will give you lists of people in your country. I would explain to the ones you choose to interview that you’re looking to find specific coping skills. This will help them work with you to put a plan of action together to bring about the changes you want.