Hello and thanks for your question.
Where parents agree after separating, any arrangement for the chilren can be put in place. If the parents cannot agree, then as a last resort, either parent can apply to the family court for a child arrangements order that says who the child will live with and how much time they will spend with the other parent.
The court decides any issue concerning children on what is best for that particular child, not on who shouts loudest. So you are absolutely right to consider the effect on your son. Obviously, every child is diifferent, and every father-son relationship is different, so you definitely DO need to consider what your son can cope with, given his upset at the two of you separating, and his current relationship with his dad, and his need to maintain that relationship, regardless of how much the two of you now dislike each other.
You are entitled to satisfy yourself that the accommodation is suitable for your boy. Ask to see the room where your son will be sleeping if you are in any doubt. When your son does go to stay with his dad, make sure his dad knows what his bedtime routine is, and that your son has all his usual toys with him. Staying with his dad should not change your son's normal routine in other ways if at all possible eg his nursery times and days should stay the same.
You and your ex need to have each other's mobiles if he needs to get hold of you while your boy is with him.
If you do have to go to court, it's very unlikely that the court would order as much as 7 nights a week in each person's house - that sounds very unsettling to me,like being constantly on the move - but especially for such a young child. However, the court WOULD expect you to promote contact between your son and your father - but maybe something like alternate weekends 2 nights staying with his dad, plus say a few hours/half a day on a Sat or Sun on the weekends he doesn't stay overnight, plus say an hour once a week early evening?
Going to court is stressful, time-consuming and expensive, so to be avoided if at all possible. You can negotiate either between yourselves, or via solicitors' correspondence, or via mediation. The family court anyway now requires the parties to have attempted mediation before it will consider an application to court. Here's where to find a local family mediation service:-
You would also benefit from some face-to-face legal advice. Here's where to find a specialist family law solicitor:-
I hope this helps and I wish you the best of luck.
Thanks and best wishes...