I just want you to know that what you are facing is not an unusual situation and you are not alone. As a senior you can look in to this issue and deal effectively. You might need to know few things and bit of support from the organizations and belief in yourself.
I would answer the question first about how to deal with difficult colleague .
You need toe stablished following things.
First decide whether you are likely to succeed in getting this ‘difficult colleague’ to change their behavior towards you by asking these questions
Has this person taken an active part in causing the problem?
Does this person consistently cause problems?
Is there a consensus that this person generally causes
If the answers are ‘yes’, Then you need to ask yourself what the chances are that this person will modify their behavior for you. The following tips may help you to decide how to proceed.
What is the difficulty?
What are the issues (specific or general, type)?
Why has the problem arisen?
Is it affecting other people?
Is it a personal or an organizational issue presenting as
a personal one?
Has anyone else had similar difficulties?
What was the situation before the current difficulty?
What has already been tried to resolve the situation?
Who could you approach for advice and support?
What should you do if you are being bullied
Once you explored the above things then you can look in to the possible solutions available.
But it is important that you should not avoid the issue hoping it will go away
You should also Try to see the difficulty from the other person’s
and Have an informal chat over a cup of coffee with that person,(I believe you might have done this already)
If the above steps did
not work don't worry about taking this issue to the line manager.
Now coming to the practical help--it is not uncommon to have anxiety
attacks,low mood.low self esteem and sleep problems. So, it is important to see your GP for a consultation and see whether you need any small dose of antidepressant to help the situation. This is important because of the past history of breakdown. If not, you can discuss your GP to consider small dose and short duration of anxiolytics medication to help you whilst you deal with this at practical level.
Most of the GP surgeries have counselors and it might be an idea to speak to them if you are not willing to consider any medications.
I wish you all the best.
I hope you find the answer helpful.