I pray only on Fridays, but I love God and believe in Him; am I not a Muslim? What should I do for being so?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

All Muslims have duties that they must do. Salah, the prayer, is one of the most important duties in Islam. Because of this importance, the Prophet Muhammad made the prayer the limit that separates Islam from Kufr. He said: “The pact between us (Muslims) and them (disbelievers) is the prayer. Whoever abandons it is a disbeliever.” [At-Tirmithi]

You mentioned that you abandoned the prayer and gave up praying any prayer save the Friday prayer. You have put yourself in a great danger. Many Muslim scholars have agreed that a person who gives up one prayer willingly becomes a Kafir (unbeliever).

Allah Says (what means): {But there came after them successors who neglected prayer and pursued desires; so they are going to meet evil.} [Quran 19:59]

Ibn ‘Abbas said: “The term ‘neglected prayer’ means they didn’t give it up totally; rather, delayed it from its fixed time.”

So, dear brother, (May Allah protect you) look at the destiny of those who pray but delay it from its fixed hours.

Allah Says (what means): {Verily, the prayer is enjoined on the believers at fixed hours.} [Quran 5:103]

You shall then prove your love of Allah by abiding by his orders.

A poet once said: (adapted) “If you were true in your love, you would have obeyed Him. The lover is obedient to the one whom he loves.”

As result, you should repent to Allah as you did before. You should also observe your prayers at their fixed times. In addition, it is better that you perform Nawaafil (supererogatory prayers) as much as possible.

Do what Allah has ordained you to do and avoid what He has forbidden for you.

Allah knows best.