Dominic Cooper says he understands why actors get romantically involved with their co-stars. The 34-year-old actor says off-screen romance is inevitable when actors spend a lot of time together during filming and portray being in love on-screen. ''There are parts where for 12 hours on that day you are portraying someone who is so in love that they are on the cusp of insanity- so you can understand that dynamic chemistry,'' Contactmusic quoted him as saying. Cooper has previously dated fellow Mamma Mia! star Amanda Seyfried. He has also been romantically linked to actresses Ruth Negga and Gemma Arterton.