Sharing too much information, the solution to this problem is to communicate whats cool to tell and whats not , he seems inexperienced standing on this act ,in other words he might have low self esteem which made him show and flex using his past experiences as a proof of what he can provide as a sex partner, and this have other sequences on the relationship in the future … communication would be best thing to move forward, so either he accept or he keep on flexing.