A poll of 1,000 young adults has found that 70% believe honest discussions about STIs are an important signal that a relationship will last the pace.
Around 66% thought meeting the parents was the most significant factor.
Not always wearing the right make up (47%), meeting friends (40%) and being given space in the cupboard to leave clothes (30%) make up the top five indicators.
The survey was carried out on behalf of the "Chlamydia. Worth Talking About" campaign. It aims to encourage people under the age of 25 to get tested for the STI.
The Populus poll also revealed the difficulty young people have in discussing sexual health-related issues with a new partner. Almost three quarters (73%) said they never raise the issues before they have sex for the first time.
Around 30% said they felt uncomfortable asking a new partner to use a condom.
Public Health Minister, Gillian Merron, said: "STIs can be a difficult subject to talk about, but it's encouraging that young couples are starting to see beyond that. The government's 'Chlamydia. Worth Talking About' campaign aims to get young people discussing STIs and saying yes to chlamydia tests."