I am afraid your case is being handled unprofessionally. It is quite normal for all males, who have not been exposed to sexual relationships in the past, to be anxious leading to purely temporary and harmless inability to achieve adequate penile erection. It is not compulsory to have sexual intercourse with your wife on the very first night! True impotence in a healthy, normal male of your age is very very rare.
Tadalafil is indicated for use in those who have organic illness such as diabetes, spinal cord injuries etc. Its misuse by normal persons like you is dangerous in the long range. It has many side effects including an adverse reaction on eyes and eye sight. Also it is not permitted to be taken with many other medicines.
Please stop worrying about sex and start your new life with a positive note, get to know your wife better, enjoy non-sexual activities. I can assure you, in no time you will find that you do not need harmful medicines to have sexual relationship.