Duties Towards Neighbor
Question :

what is our obligation towards the neighbor?

Answer :

It is prohibited to harm the neighbors, it is highly recommended to be kind with the neighbors and to deal with them in a good way.

Transgression against believers
Question : I committed a big sin and had sex outside the marriage, and after that I am now not able to concentrate, everything gone upside down, and I am feeling so guilty about myself, only one thing is coming in my mind that I cannot live with this guilty anymore and want to finish myself.
Answer : It is not correct to commit a greater sin because of committing a lighter one, since committing suicide is greater than adultery. You should repent from what you have done as Almighty Allah forgives all sins.

You can guard yourself by getting satisfied through marriage whether it is permanent or temporary. May Allah help you pass this hardship.
Transgression against believers
Question : Are there any cases/situations in which Islam permits suicide?
Answer : Islam does not allow suicide in any way or form.
Question :

Me and my friend had a fight and we are not talking to each other for the past two years. Someone told me that this is prohibited. Is that true?

Answer :

Based on compulsory precaution, one should not desert a believer for more than three days, even if the latter was wrongful to him. It is sufficient to satisfy this obligation by greeting him (e.g. saying 'salam alaykum'). If the other party insisted on the abandonment, he will become the deserter.
This prohibition has three exceptions:
First: if the desertion was to forbid the wrong.
Second: if the desertion would lead to a benefit that the Sharia recommends, like - for example - if desertion leads to paying attention towards a truth that could remain hidden without such desertion, or similar cases.
Third: if the reestablishing the relationship would lead to demeaning oneself. One should be careful in not confusing arrogance and anger with self-demeaning.