It seems that your recent move has been difficult. It is possible that you and your girlfriend are in the midst of a sustained adjustment period. Moving to a new country is a major life change. Moving from your native country meant leaving the life that you knew, your job, your friends and family, etc. These are all significant losses. You may be grieving those losses. For many people, such a move would be traumatic. It could lead to feelings of disillusionment, confusion and depression.
Other aspects of this issue may be related to the fact that perhaps moving to a new country was not what you thought it would be. You may have had unrealistic expectations. Your new reality may be inconsistent with your expectations. If so, the incongruence between what you thought life would be after the move and what it is may be contributing to the problem.
Another aspect of this problem may be that you and your girlfriend are reinforcing each other’s negative feelings. Happiness is thought to be contagious. So might depression and negative thoughts, at least in this specific situation. You and she may be having difficulty decreasing the feelings of depression in part, because neither party has a sense of hope or happiness. In this situation it may be that depression begets depression.
To answer your specific question, yes, I do believe that it is possible for you and your girlfriend to return to your normal state of psychological functioning. The most efficient way to do this would be to seek help from a mental health professional. Given the fact that you have contemplated suicide, I would not recommend attempting to deal with this problem on your own.
Professional help could greatly benefit both you and your girlfriend. A mental health professional can help break the cycle of depression and isolation. I am not familiar with the mental health services in the UK, so unfortunately I am unable to provide a link to a specific agency or treatment center.
I would also like to add the thought that perhaps you have underestimated the process that you have begun. Perhaps you thought that moving to the UK and finding a decent job was the process, the whole process but perhaps it is only part of the process. Perhaps you are only a good healthy step along the way. Maybe the future holds more career development, starting a business, getting more education, etc. Be proud that you are succeeding.
I hope that you are able to get the help you need. Please take care. I wish you well.