Bismihi ta'āla
If one feels they are "unprepared" for marriage, then should work on preparing themselves, and make that their fundamental priority. Nothing is better than getting married.
Pursuing temporary marriage is not going result in long-term solution, so it is good they do not wish to pursue it.
Sexual lust is natural, given to us by Allah ta'ala for many benefits. We just need to regulate it, and control it when needed. We are all prone to becoming weak in our self-control, and Shaytan could overcome us. However, with jihad al-nafs, and resisting haram urges, one will see wonders.
Strong focus on acts of worship is one effective method of coping with lust, especially prayer and connecting with the Lord.
Avoid anything that leads to rising of lust, like what you see, or hear. Try to fast, as the Prophet (s.a.w.) advised.
Occupy yourself with various activities. Try not to be alone, and interact with family members more.
The element of dua is also very important. Immerse yourself in supplications, beseeching Allah and imploring Him to keep you pure, and grant you a righteous spouse.
And Allah knows best
