Why when im alone masturbating watching films my penis gets big but only for a couple of seconds its hard? but when i facetime my girl it gets big and stays hard?

Normal: What you described is normal. Have a healthy diet, exercise 30 minutes/day, drink plenty of water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. For nutrition: http://www.choosemyplate.gov/. Get HPV and Covid vaccines. Wish you good health! Safe sex: https://www.hopkinsmedicine.org/health/wellness-and-prevention/safer-sex-guidelines