Ex Boyfriend

Me and my ex broke up in 2018. Since then he has had 1 girlfriend and I have had 2 boyfriends. My last relationship was extremely toxic and I constantly felt like I was still in love with my ex but told myself it was just because I was in a bad relationship. However now I’m in my third relationship, it started off well but the feelings about my first boyfriend have been creeping back in lately and I feel like I’m really just not ready to let him go. If I ever see him across from me in the pub or something I get anxious butterflies. He has been with his new girlfriend for 5 years now but always asks my friends how I’m doing when he sees them and recently asked where I was when we were attending the same event. What do I do?