Anal!!!! Help

Okay, this may be weird but whatever. So I used to date a guy for about 4 years. I did anal with him twice, I wasn't sure about it but I know he wanted to. It hurt, I couldn't find a way to enjoy it but I also didn't enjoy pleasing him as much he was unfaithful and a liar and just an ass. I've now been dating this guy for about 6 months but he's the love of my life. I'm absolutely and completely in love with him I swear I'm going to marry him. Today we were joking and made a joke about doing anal. However that joke turned serious and we agreed we'd both do it. All I can think about is how it hurt with my ex and my current boyfriend is definitely thicker and better 👅👅 my question is what can I do to relax myself and enjoy it for myself and for him. I'm worried he will hurt more because of his size. I'm 18 going on 19