The Shape of Things (2003) on Netflix

Adam Sorenson is a simple, insecure and shy student that works half period as a security guard of a museum and in a rental. He meets the anarchist and transgressor student of Arts Evelyn Ann Thompson trying to paint a penis in an important statue, and after arguing with her, in the end they schedule a dinner. Evelyn becomes his girlfriend and he introduces his best friends, Jenny and Phillip, to her. As long as they stay together, Adam's behavior changes and his appearance and confidence improve influenced by Evelyn. He has an affair with Jenny, betraying and lying to Evelyn and to Phillip, and destroying their friendship. When Evelyn presents her thesis for the Master degree, Adam is surprised with revelations.