Ex and new boyfriend?

About 2 months ago I broke up with my ex of three years. We both started dating at 15. We both made mistakes and have a history. Towards the end I was feeling unhappy because of things that happened and a big argument triggered me to break up suddenly. My coworker that has had a crush on me for months always wanted me to give him a chance because he knew he could treat me better. So about a week and a half afterward we started talking. We hit it off and he sees a future with me..he’s like 5 years older and more mature than my 19 yr old ex. He does treat me with more respect and it’s refreshing to have a clean slate. The thing is i keep dreaming about my ex and thinking of him. Today when I went to give my ex his things back we had a conversation about the plans he had with me and when he gave me a hug, all I wanted to do is start over with him again and try to work things out. he gave me a box and it had a picture from our first date. He wrote “I’ll always love you and wait for you”. After he left I started crying and now it’s messing with my head and emotions. I really don’t know what to do but I do know the new man I’m talking to is the type to not give a second chance so I need to get my emotions straight real quick. Any advice?