Ok, but we don't usually use "come" or "come in" with the acting metaphor. I was trying to seduce this girl but my friend interrupted my effort(s) and destroyed my chances. He told her … If you want to keep the idea of "act", you could use something like "made an appearance" or "entered the scene". My friend entered the scene in the middle of my act and ...

(already talking about "him") ... "I was trying to persuade this girl to go with me, but he came during the middle of my act and destroyed it. He told her I was married and had three children." I would say "he came during" instead of "he came in" Mich https://www.italki.com/michelle

Gregory is right! Unless before you said your sentence, you were already talking about "him".

In the first sentence the use of the pronoun "he" is a problem. You can only use a pronoun if the listener or reader first knows who "he" is. Here is a better way to say it: I was with my friend Vladimir when I saw a girl I met earlier in the day. I was trying to persuade this girl to go with me, but he (Vladimir) came in the middle of my act and destroyed it. He told her I was married and had three children." Good luck Alyosha!