My(24f) current boyfriend(23m) wants my exes number to "put his mind to rest" about anything going on.

My current boyfriend wants my exes number to "put his mind to rest" about anything going on.

Essentially my (24f) boyfriend (call him A) (23m) were together for 3 years. We broke up around March last year (2025) as i felt asthough I didn't trust him anymore and our spark was gone, he wasn't putting im the effort. Despite this i told everyone that i know we will get back together. We have a connection I've never felt with anyone before. In August I got together with another guy (call him B). Me and B dated for a while through to december. Despite a brief "breakup" in October as i started seeing A again and felt guilty. However I did not recognise that A was hoping to reconcile so I started seeing B again. The same happened in December. On the 21st of December A called me saying he is serious and wants to try again, this means he doesnt want to "be double timed". After this I called it quits for real with B. However I had booked tickets for me and my sister to see a band late January. B also bought tickets and suggested a dinner, with my sister, beforehand. I thought why not. There's nothing going on and its simply a dinner. Looking back on this i realise it was a huge mistake. Not only was he just rude to me the whole time but it has caused A to no longer trust me. I didnt tell A at the time that i was meeting B for dinner as, again, it didnt seem like anything important, i have never wronged A before and i thought itd just make A angry unnecessarily. A found out about this dinner a week ago but doesnt believe that it was just a dinner and says I have lied to him. I have told him that nothing happened between B and I and we met just for dinner with my sister beforehand and the fact he was rude throughout. However A is now saying he doesnt trust me and is refusing to believe that I'm telling the truth. He wants to have Bs phone number "to find out the truth" and if I have nothing to hide then what's the issue. Thing is A is PISSED. I dont think it'd be right for him to contact B. Neither of them liked eachother and I think all it will cause is more issues. I dont think B will answer any text that A sends, if he does he is either going to be rude to A or B is going to lie about something happening to get back at me for "leading him on" although I told B from the go that Im not looking for anything serious. Either way I know A will be pissed. I just want A to try to trust me when I say nothing has happened between B and I since me and A got back together officially. Genuinely what am I meant to do? I also feel super uncomfortable giving out someone's phone number and A doesnt want me contacting B to ask if i can share his number. I feel stuck. I love A SO much and flew to Canada to see him during his training just last week, spending most of my paycheck to do so, but this is feeling very controlling and as though he is making excuses to try to not trust me. If I am putting in the effort to trust him again why cant he do the same for me?

Tl;dr my current boyfriend doesnt believe that nothing is going on with my ex and wants my exes phone number to check with him