There are appropriate times to bring up certain things in a relationship, and certain things you shouldn’t discuss until you’re ready, but there is one thing that, if it comes up, you need to be honest about it: if you’re still friends with an ex.
And, yes, it’s possible to still be friends with your ex. Anybody who insists otherwise either has never had a mutual break-up or just lives for drama. Granted, no breakup is ever easy, even if both parties know they have to move on, but it is possible to get out of it without screaming fights and resentment. Hurt, not so much, but you can at least avoid the really bad parts if you’ve both grown-ups.
Of course, in some situations, heck, many situations, it can be hard or even impossible for you and an ex to stay in touch or be amicable. But it happens, and it happens more often than people think.
So, if your ex is still in your life, and your current beau is going to meet him at a party or something, lay it out for him. And do it for two reasons.
1) How a guy handles being around somebody you used to date is a fairly important litmus test as to whether or not to keep dating him. If he’s got jealousy issues, hang-ups about you having a life before he met you, or other problems that will complicate your relationship, this will bring it out. But if he’s a grown adult, he likely won’t have a problem with it and even realize it speaks well for you. After all, if you can break up with somebody and they don’t hate you, that’s an achievement in maturity.
2) He’s going to find out eventually. It’s not like you and your ex dating was a big secret nobody knew about. Presumably you told your friends, among who you number your ex. If it comes off like you were hiding him, the best case scenario is that he thinks you’re not being honest. The worst case? He thinks your ex is not as “ex” as you claim.
Honesty is usually the best policy, and in this case, especially so. Be up front about your life: after all, you’ve got nothing to be embarrassed about.