In his response to this issue, Dr. Rajab AbuMaleeh, Ph. D. in Sharia, stated that:
A Muslims should never despair. If it happens that due to your weakness that you return back to your sin, repeat your repentance sincerely and with a great determination not do this sin again. Allah forgives us as long as we repent, but if we stop repentance, we will deserve His sever punishment. Of course breaking the promise is a sin that requires tawbah, but Allah loves those who constantly repent. So I advise you to keep repenting and try to be more sincere in each tawabah until you reach that tawbah that helps you not repeat the sin again.
We are in a conflict with our selves and with the Satan and we should not surrender. Keep on your Prayer, since it is the way to Allah and His forgiveness. It is the true sign for that you are a good Muslim.
Salah (ritual prayer) occupies the key position for two reasons. Firstly, it is the distinctive mark of a believer. Secondly, it prevents an individual from all sorts of abominations and vices by providing him chances of direct communion with his Creator five times a day. In prayer he renews his covenant with Allah and seeks His guidance again and again: Allah Almighty says: “You alone we worship and to You alone we turn for help. Guide us to the straight path.” (Al-Fatihah: 5-6)
Actually Salah is the first practical manifestation of Faith and also the foremost of the basic conditions for the success of the believers: “Successful indeed are the believers who are humble in their prayers.” (Al-Mu’minun: 1-2)
The Prophet (peace and blessings be upon him) emphasized the same fact in a different way, saying: “Those who offer their Salah with great care and punctuality will find it a light, a proof of their Faith and cause of their salvation on the Day of Judgment.”
In addition to keeping your Prayer, you have to search for a righteous company that helps you to continue in the path of Allah and advice you when you go astray.”