Can an ex who's now a friend come to the wedding?

Richard and Lisa are getting married next month. Lisa has invited her very close friend, Steve. Seven years ago, Lisa and Steve dated. Since then, they have turned into very good friends, and Lisa wants him to be at her wedding. Richard doesn’t want him at the wedding, thinking that Steve will ruin the wedding and maybe even steal Lisa. Lisa swears that she has no more romantic feelings for Steve, and would never try the relationship by doing things such as crying on Steve’s shoulder after a fight with Richard.

Who’s side are you on?

Does that change if Steve told Lisa he was still in love with her at her bachelorette party?